Leah appears to have lied about her age all her life.  It has never been unusual for women to lie about their age, and some women often insisted their husbands, even their older children, do the same, so as to support their younger age (my own grandmother did so).  Leah just seems to be a most spectacular case.  There also seems to be some census-taker error thrown in.  Generally, the age in the records that makes the woman the oldest is the correct one.

.  Moses KERSTETTER, b. 1841/2 or Mar 1847
.  Hanna KERSTETTER, b. 1843/4
.  Zeone KERSTETTER, b. 1845/6
.  Aaron D. KERSTETTER, b. 18 Jun 1848
.  Henry D. KERSTETTER, b. 18 Jun 1850; d. 25 Aug 1872; bur. Dressler Cem., Juniata Co., PA
.  Jacob Dressler KERSTETTER, b. Feb 1855
.  William H. KERSTETTER, b. 1854/5
.  Amanda KERSTETTER, b. 1855/6 or 1858/9
.  Peter Dressler KERSTETTER, b. 19 Jun 1861
.  Samuel KERSTETTER, b. 1859/60

I presume the "infant" in the 1850 census is Aaron.  Henry may be William H.

1.  Marriage Record:

2.  1850 Census Index/Images (online at Ancestry.com; Image #22 of 44):  Greenwood Twp., Juniata Co., PA, p. 312B, 2046/2076, enumerated 4 Nov 1850, official enumeration date 1 Jun 1850 (extracted by Diana Gale Matthiesen):¤

Henry Castetter	26	M		Farmer	800	Penna
Leah Castetter	24	F				"
Moses Castetter	8	M				"
Hanah Castetter	6	F				"
Zeone Castetter	4	F				"
Infant	1	M				"

Leah is very young to have a child eight, or even six, years old — for that matter, so is Henry, if only 26.  Iwonder if the older children are "family orphans" whom they've taken in.  Listed next door to Adam (æ 60) & Lydia (æ 55) CASTETTER, who are almost certainly John Henry's parents.

3.  1860 Census Images (online at Ancestry.com; Image #13 of 21):   Mahontongo P.O., Susquehanna Twp., Juniata Co., PA, p. 795, PN 235, 1621/_, enumerated 2 Aug 1860, official enumeration date 1 Jun 1860 (extracted by Diana Gale Matthiesen):¤

John Carstetter	30	M		Farmer	2000	900	Penna
Louisa Carstetter	27	F					"
Wm H	5	M					"
Franklin Boner	11	M					"

At first, I didn't believe this household could possibly be our subjects, though I could find them nowhere else.  Then I saw they were listed next to Widow Lydia KARSTETTER (æ 60), John Henry's probable mother, just as they were in 1850.  So, despite my misgivings, I guess these are our subjects.  There are a number of possibilities here, the most probable one being that the enumerator botched the record (there are known cases of enumerators fabricating records out of sheer laziness).  There is also the possibility that the three older children with them in the 1850 census weren't theirs.  In fact, the lack of correspondence between ages and children from year to year suggest John & Leah may have had few or no children, themselves, but like many childless couples, took in all the extended family's orphans.

4.  1870 Census Images (online at Ancestry.com; Image #7 of 24):  Mohontongo P.O., Susquehanna Twp., Juniata Co., PA, p. 465A, PN 7, 48/48, enumerated 13 Aug 1870, official enumeration date 1 Jun 1870 (extracted by Diana Gale Matthiesen):¤

Castetter John	47	M	W	Farmer	4000	675	Pa
_________ Leaah	40	F	W				Pa
_________ Moses	22	M	W	at home			Pa
_________ Aaron	20	M	W	F $			Pa
_________ Henry	18	M	W	F $			Pa
_________ Jacob	16	M	W	Laborer			Pa
_________ Amanda	14	F	W				Pa
_________ Peter	11	M	W				Pa
_________ Sanuel	10	M	W				Pa

This enumerator frequently used "$" in the Occupation field; I haven't a clue what it was intended to represent.  Listed next to Henry CASTETTER, who is next to Jas/Jos CASTETTER, on one side; and, on the other side, next door to John CUPP, who is next to Michael STROUP. 

5.  1880 United States Census and National Index (LDS Family History Resource File: CD-ROM Library):¤

Census Place: Susquehanna, Juniata, Pennsylvania
Source: FHL Film 1255137; NARA Film T9-1137; Pg 364B
	Relation	Sex	Marr	Race	Age	Birthplace	Occupation	Fa	Mo
Henry KERSTETTER	Self	M	M	W	60	PA	Farmer	PA	PA
Leah KERSTETTER	Wife	F	M	W	59	PA	Keeping House	PA	PA
Jacob KERSTETTER	Son	M	S	W	26	PA	Cabinet Maker	PA	PA
Amanda KERSTETTER	Dau	F	S	W	21	PA	At Home	PA	PA
Peter KERSTETTER	Son	M	S	W	19	PA	Works On Farm	PA	PA

6.  1890 Census:  the 1890 Census Population Schedules were destroyed.

7.  Perry Historians, Newport, PA, compilers.  Dressler Evangelical Churchyard (United Methodist), Susquehanna Twp., Juniata Co., PA (online at the Juniata County PAGenWeb site; contributed by Pauline Shunk):

KERSTETTER,

Henry D.

s/o Henry & Leah

June 18, 1850

Aug 25, 1872

8.  LDS.  Family Search: Internet Genealogy Service: Pedigree Resource File (index to CDs, online at FamilySearch.org).

9.  Messages in the Dressler Family Genealogy Forum (online at GenForum.com).

10.  WorldConnect / Ancestry World Trees (online at RootsWeb.com/Ancestry.com).