It's unlikely that the census-taker made his rounds before Jan 5th, so John should have been 36 in the 1850 Census.  Apparently, there really were two daughters named "Martha Jane," which makes one wonder if Abijah's mother wasn't named Martha Jane.

Abijah and Elizabeth lived together, and had three children together, before they were married.  Son George was born the day Abijah's divorce was granted.  Could it have been an event so emotional for Elizabeth as to trigger her labor?  If you put yourself in Elizabeth's situation, in the culture of her day, the prospect that Abijah would finally be able to marry her and "make an honest woman of her" would definitely be such an emotional event.

1.  Jordan R. Dodd, ed.  1993.  Kentucky Marriages:  Early to 1850.  Liahona Research, Orem, UT (Broderbund CD-229):

Hightower, Abijah	Saunders, Alaska	Nov 16, 1811	Logan Co.
Hightower, Abijah	Jones, Elizabeth	Apr 19, 1827	Todd Co.

2.  LDS.  Family Search: Internet Genealogy Service:  IGI - International Genealogical Index (online at FamilySearch.org).

Abijah Whittier HIGHTOWER Birth: 4 May 1836, Todd, Kentucky Father: Abijah HIGHTOWER; Mother: Elizabeth JONES Source: patron submission

3.  Census Index:  U.S. Selected Counties, 1790 (Broderbund CD-311):  not found, but no VA, KY, or TN census is extant.

4.  Census Index:  U.S. Selected Counties, 1800 (Broderbund CD-312):  the 1800 KY and TN censuses were destroyed, so tax lists are substituted on this CD.

1805 Tax List	Hightower, James	TN	Anderson Co.
1805 Tax List	Hightower, Abijah	TN	Anderson Co.

5.  Census Index:  U.S. Selected Counties, 1810 (Broderbund CD-313):  no Austin, no Oldham, no Abijah, anywhere; no HIGHTOWER in Christian Co., KY.  The 1810 TN census was lost.

6.  1820 Census Index/Images (online at Ancestry.com; Image #5 of 19 — indexed as "H. Hightower"; extracted by Diana Gale Matthiesen):

1820

KY

Todd Co.

p. 127/416

A. Hightower

100010-00001-0-100

no slaves

These data indicate:

No. & Sex	Age Class	Therefore Born	Individuals Inferred
1 male	9 or under	1810-1820	= John (b. 1814)
1 male	26-44	1775-1794	= Abijah (b. 1782/3/4)
1 female	45 or over	in or bef. 1775	= ?
1	person engaged in agriculture

Alasha and the two girls have left.  Was the older woman Abijah's mother?  Or was she hired help, brought in to take care of John and the domestic duties?  Or is this Elizabeth, tallied in the wrong column?  They are living between George JONES (Elizabeth's father, perhaps?), on one side, and Nancy SCROGGINS, on the other side.

7.  1830 Census Index/Images (online at Ancestry.com; Image #29-30 of 68; extracted by Diana Gale Matthiesen):

1830

KY

Todd Co.

p. 372

Ln. 17

Abijah Hightower

210 100 100 - 010 100 000

no slaves

These data indicate:

No. & Sex	Age Class	Therefore Born	Individuals Inferred
2 males	4 or under	1825-1830	= son = George (b. 1826)
1 male	5-9	1820-1825	= Andrew (b. 1822)
1 male	15-19	1810-1815	= John (b. 1814)
1 male	40-49	1780-1790	= Abijah (b. 1782/3/4)
1 female	5-9	1820-1825	= Martha (b. 1823/4)
1 female	15-19	1810-1815	= ?
0 female	30-39	1790-1800	= Elizabeth (b. 1799/1800)

They missed Elizabeth.  Or did the census-taker tabulate her in the wrong column?  Surely she was not lying about her age to that degree!  Living next door to Matthew STOKES, father of Annie STOKES, who later married Abijah's son, John. 

8.  1840 Census Index/Images (online at Ancestry.com; Image #33-34 of 72 — mis-indexed as being in "Todd City" because the "Cty" in "Todd Cty" was misread as "City" [there's no such place as Todd City]; extracted by Diana Gale Matthiesen):

1840

KY

Todd Co.

p. 17 | pp. 254B-255A

Ln. 17

Hightower A

301 100 010 - 010 100 100

no slaves

0400000

These data indicate:

No. & Sex	Age Class	Therefore Born	Individuals Inferred
3 males	4 or under	1835-1840	= Mack (b. 1839) = Abijah (b. 1836) = William (b. 1833/4)
1 male	10-14	1825-1830	= George (b. 1826)
1 male	15-19	1820-1825	= Andrew (b. 18220
1 male	50-59	1780-1790	= Abijah (b. 1782/3/4)
1 female	5-9	1830-1835	= Mary (b. 1831)
1 female	15-19	1820-1825	= Martha (b. 1823/4)
1 female	40-49	1790-1800	= Elizabeth (b. 1799/1800)
4	persons employed in agriculture

9a.  1850 Census Index/Images (online at Ancestry.com; Image #20 of 100 — indexed "Abigah"):  District No. 1, Todd Co., KY, p. 204B, 140/141, 29 Jul 1850 (extracted by Diana Gale Matthiesen):

Abijah Hightower	66	M	Farmer	300	NC
Elizabeth	50	F			VA
Mary	17	F			Ky
William	16	M			"
Abijah Jr	14	M			"
McReynolds	10	M			"
Mary	11/12	F			"

Who is baby Mary?  A grandchild?  Listed next to son, Andrew Jackson HIGHTOWER.

9b.  1850 Census Index/Microfilm (online at GenealogyLibrary.com — indexed as "Alaska Hightour"):  Lynn Twp., Posey Co., IN, pp. 216AB, 706/706, enumerated 3 Sep 1850 (extracted by Diana Gale Matthiesen):

Hudson Causey	52	M	farmer	1000	N.C.
Martha    "	34	F			Tenn
[six children of Hudson & Martha]
Alasha Hightour	64	F			N.C.

10a.  1860 Census Images (online at Ancestry.com; Image #49 of 170):  Elkton P.O., Todd Co., KY, p. 719, PN 49, 339/339, enumerated 2 Jul 1860, official enumeration date 1 Jun 1860 (extracted by Diana Gale Matthiesen):

A Hightower	86	M		F	1000	200	NC
E Hightower	65	F					Va
Mack	22	M		F			Ky

Wow, are these ages off!  Listed next to son, William Robert HIGHTOWER, who is next to son, George Washington HIGHTOWER, who is next to son, Andrew Jackson HIGHTOWER, in one direction; and, in the other direction, listed two households from daughter, Mary (HIGHTOWER) RUDD.

10b.  Census Index:  U.S. Selected Counties, 1860 (Broderbund CD-318):

1860	Littlepage, Louis	IL	White Co.	Burnt Prairie P.O.	p. 592
1860	Littlepage, Louis	IL	Whiteside Co.	Burnt Prairie P.O.	p. 592

Alasha (SAUNDERS) HIGHTOWER is said to be living in Illinois with her grandson, Lewis LITTLEPAGE.  Why there are two versions of this record on the CD is a mystery.  There are, indeed, both White and Whiteside Cos. in Illinois, but according to the GNIS (U.S. Geological Survey.  GNIS:  Geographic Names Information Service, online database), Burnt Prairie is in White Co.

11.  Willard Rouse Jillson.  1925.  The Kentucky Land Grants. Filson Club Publ., Louisville, KY (online at Ancestry.com; Broderbund CD-650):

Vol. 1, Pt. 1, Chap. VI, Kentucky Land Warrants, 1816-1873
Pg	Grantee	Acres	Book	Pg	Date	County	Watercourse
589	Hightower, Abijah	125	F	107	5-20-1819	Christian	Elk Fk Red R

Abijah almost certainly paid for his land with a warrant received for fighting in the War of 1812.  Further research could confirm it.

12a.  A.B. Willhite.   [n.d.]  Christian Co., Kentucky, Tax List, 1810-1813.   (Self-published; available from author at 4396 Coopertown Rd., Russellville, KY 42276, or from the Christian County Genealogical Society, Hopkinsville, KY).  Abijah HIGHTOWER not found.

12b.  A.B. Willhite.   [n.d.]  Christian Co., Kentucky, Tax List, 1814-1818.   (Self-published.  This book is out of print.  I do not have a copy.  If you have one to sell, please contact me.)

12c.  A.B. Willhite.   [n.d.]  Christian Co., Kentucky, Tax List, 1819-1823.   (Self-published; available from author at 4396 Coopertown Rd., Russellville, KY 42276, or from the Christian County Genealogical Society, Hopkinsville, KY).

Pg. in Willhite	Year	First Name	Last  Name	A	B	C	D	Acres	Watercourse
30	1819	Abijah	Hightower	1			1
	1820-23	[not found]
Legend for numerical data: A = White Males 21 or over; B = Blacks over 16; C = Total Blacks; D = Horses

He is the only HIGHTOWER in the book and occurs only in the one year.  As expected, Abijah drops off the Christian Co. tax rolls with the formation of Todd Co. in 1820.

13.  Karen Combs, transcriber.  1840 Tax List - Todd County, Ky (online at the Todd County KYGenWeb site):

Pg.	Name	Acres	Watercourse	Value
19	Hightower, Alijah	100	Elkfork RR	100

14a.  Broderbund.  World Family Trees.  Vol. 5, Pedigree #1090, which cites the next source.

14b.  Ruth Ann Hightower Smith.  1995.  Todd County, Kentucky, Family History.  Turner Publ.

Abijah Hightower was one of the earliest Hightowers in this area.  According to his tombstone and census records, he was born in North Carolina Aug. 9, 1782.  He and a Joshua Hightower were listed in the 1803-1804 Taxpayers list in Knox County, TN, and he and James Hightower were listed as taxpayers in Anderson County, TN, in 1805.  They were in the Knox County area until at least 1807; however, Abijah, James and George Hightower appeared as taxpayers in Logan County, Ky, in 1811.

15.  Robertson County, Tennessee.  Court Minutes:  Book 4, 1815-1818. (courtesy of Ruth Hightower Smith via Lisa Hightower):

"...May term, 1816, David Smith got 50 acres of land from Moses Shelby, witnessed in open court  by Abijah Hightower."

16.  WorldConnect (online at RootsWeb.com).

17.  LDS.  Family Search: Internet Genealogy Service:  IGI - International Genealogical Index (online at FamilySearch.org).

18.  Emails from Steve Watson, Joyce Ubl, Ruth Hightower Smith.