The average male is age 23 at first marriage, hence my estimate that our subject was born ca. 1743.

The average female is age 19 at first marriage, hence my estimate that our subject was born ca. 1747.  She cannot have been much older because she had a child in 1788, and most women have had their last child by the age of 43 (average age for the onset of menopause is 41).

By 1800, all the remaining children had moved to Bourbon Co., KY, either before or with their mother:

2.  Sarah CORBIN, b. 1769/70, PA; m. 1788, Thomas MARSH, Jr., s/o Thomas MARSH & Sophia CORBIN
3.  Abraham CORBIN II, b. ca. 1775; m. 1798, Eleanor BOSLEY, d/o James BOSLEY & Temperance MARSH, d/o Thomas MARSH & Sophia CORBIN
4.  Eleanor CORBIN, b. ca. 1778; m. 1797, Beal MARSH, s/o Thomas MARSH & Sophia CORBIN
5.  Nicholas CORBIN, b. 1783/4
6.  Nathan CORBIN, b. 3 May 1788; m. 1811, Mary HILL

1a.  Robert Barnes.  1978/93.  Maryland Marriages, 1778-1800.  Genealogical Publ. Co., Baltimore, MD (Broderbund CD-195).

p. 40	Corbin, Abraham, 4 Dec. 1766, Rachael Marshall	2 BA-230
p. xi	2 BA - St. John's and St. George's Parish; copy made by Harrison, at MHS [Maryland Historical Society].  (Despite the title of the manuscript, the records are chiefly those of St. John's Parish.)

1b.  Marriage Index:  Maryland, 1655-1850.  Liahona Research, Orem, UT (Broderbund CD-224):

Corbin, Abraham

Marshall, Rachael

Dec 4, 1766

Baltimore Co.

2.  St. James Parish Register, Maryland, 1787-1815 (online at Ancestry.com):

CORBIN NATHAN, b. to Abraham and Rachel, 5/3/1788

3.  1790 Census Index/Images (online at Ancestry.com; Image #15 of 55; extracted by Diana Gale Matthiesen):¤•

1790

MD

Baltimore Co.

Patapsco Lower Hundred

Roll M637_3

p. 153

Ln 21

Abraham Corbin

1-3-2-0-8

These data indicate:

Gender and Type	Age Class	Therefore Born	Individuals Inferred
1 free white males	16 or over	in or bef. 1774	= Abraham (b. ca. 1743)
3 free white males	15 or under	1774-1790	= Abraham (b. ca. 1775)  = Nicholas (b. 1780-84) = Nathan (b. 1788)
2 free white females	all ages	in or bef. 1790	= Rachel (b. ca. 1747) = Eleanor (b. ca. 1778)
8 slaves	all ages	in or bef. 1790	= ? ? ? ? ? ? ? ?

No room here for Thomas, suggesting he was older than his siblings and had left the nest, as had Sarah.

4.  Census Index:  U.S. Selected Counties, 1800 (Broderbund CD-312):

1800 Tax List

Cobin, Rachel

KY

Bourbon Co.

Also in Bourbon County:  Abram, James, and William CORBIN, plus son-in-law, Beale MARSH.

5.  Robert W. Barnes.  1989.  Baltimore County Families, 1659-1759.  Genealogical Publ. Co., Baltimore, MD (Broderbund CD-195):

p. 135

CORBIN, ABRAHAM (5), s. of Edward (3) and Jane, b. 7 Sept. 1722 in St. Pauls Par., d. c. 1798; prob. the Abraham who m. Rachel Marshall on 4 Dec. 1766; had iss.: ABRAHAM; THOMAS; NICHOLAS, by June 1805 was in Bourbon Co., Ky., when as one of the heirs of Abraham Corbin, dec., he sold pt. The Valley of Jehosophat to Joshua Marsh; NATHAN; SARAH, m. Thomas Marsh, Jr.; ELEANOR, m. Beale Marsh  (131; 133; 231-WG#56:122; 231-WG#86:252).

For reasons given at the top of this page, I do not believe the Abraham CORBIN who married Rachael MARSHALL was the son of Edward & Jane (WILKINSON) CORBIN.  I do wish Barnes had not suggested a connection he hadn't documented because we will be forever stamping out this error.

6.  LDS.  Family Search: Internet Genealogy Service: International Genealogical Index (IGI).

Abraham-Abram CORBIN Death: 7 Oct 1793, <>, Baltimore, Maryland Father: Nicholas CORBIN; Mother: Eleanor Source: patron submission

Would that this information had been documented because it's probably correct.

7.  Mrs. H. K. McAdams.  1929.  Kentucky Pioneer and Court Records.  Lexington, KY (online at HeritageQuest at Genealogy.com):

p. 81

MARYLAND CORBIN FAMILY (Furnished by Mrs. Effie S. Honson, of Ventura, California, to Mrs. J. W. Marr, Lexington, Ky.) NICHOLAS CORBIN — Came to Baltimore Co., Md. in 1671. (Authority, "Early Maryland Settlers List." "Annapolis land office records. Vol. XVI., page 533."  Alice, wife of Nicholas Corbin, 2nd., mar. John Barrot.  (Annapolis Md. Inventories and Accounts, XX, page 47). Children of Nicholas and Alice Corbin, 1, Elizabeth (mr. Roberts); 2. Mary (mar. Gostwick); 3, Edward (mar. Jane Wilkinson, a daughter of Wm Wilkinson, 1718). Children of Edward and Jane Corbin: 1, Nicholas; 2, William Wilkinson Corbin, died; 3, Abraham Corbin; 4, Phyllis Anna Corbin; 5, Providence Corbin; 6, Unity Corbin; 7, Edward Corbin, Jr.  Abraham Corbin, son of Edward and Jane, mar. Rachel Marshall.  Abraham was born Sept. 7, 1722, St. Paul's Parrish, Baltimore, Co., Md.  Married Dec. 4, 1766, (see rec. St. John's). Their children (LIb. W. G. No. 56, page 122. Mentions all these children and widow, Rachel): Abraham, Thomas, Nicholas, Nathan, Sarah (mar. Thomas Marsh, Jr.), Eleanor (mar. beale Marsh).  All six of these came to Kentucky.

Nicholas made the crossing with his first wife, Elizabeth, and daughters Elizabeth and Mary, so Alice was not the mother of these children.  Alice does appear to have been Edward's mother.  For reasons given at the top of the page, I do not believe the Abraham who was son of Edward is the one who married Rachael MARSHALL.

8.  Broderbund.  World Family Trees.  Vol. 40, Pedigree No. 356.

9.  WorldConnect (online at RootsWeb.com).  A file there has daughter Sarah born in 1760, which does not jibe with her parents having married in 1766 and her age in the 1850 census, which indicates a birthyear of 1769/70.