John's age was more likely correct in the earlier (1840/50/60) censuses, so his birth year is almost certainly 1829, not 1832 (n.b., in the 1840 census, John's parents had only one son born after 1830, and it appears that son was James, not John).

1.  Marriage Record:

2.  1850 Census Every-Name-Index/Images (online at Ancestry.com, Image #30 of 33):  Litchfield Twp., Hillsdale Co., MI, Roll M432_351, p. 432B, 221/228, enumerated 4 Oct 1850, official enumeration date 1 Jun 1850 (extracted by Diana Gale Matthiesen):

William Stoddard	29	M		Farmer	1300	NY
Julia E Stoddard	27	F				NY
Julia E Stoddard	3	F				Mich
Eugene Stoddard	2	M				Mich
Charles Eggleston	14	M				Mich
Henriette Eggleston	11	F				Mich
John Roberts	21	M		Farmer		Mich

Julia's maiden name was EGGLESTON (see her family group sheet), so there's no obvious family connection here, though John's father was living near a Harry EGGLESTON in the 1840 census.

3.  1860 Census Every-Name-Index/Images (online at Ancestry.com, Image #36-37 of 40):  Sylvanus P.O., Allen Twp., Hillsdale Co., MI, Roll, pp. 432-433, PN 36-37, 271/271, enumerated 11 Jun 1860, official enumeration date 1 Jun 1860 (extracted by Diana Gale Matthiesen):

John W Roberts	31	M		farmer	3000	275	Mich
Sarah	24	F					NY
Miles Warren	17	M					Mich

John's middle initial is clearly "W," and he is indexed "John W."

4.  Library of Michigan 1870 Census Index and Images (online at the Library of Michigan [link died]):  Hillsdale P.O., City of Hillsdale (Ward 4), Hillsdale Co., MI, p. 346B, PN 4, enumerated 16 Jun 1870 (extracted by Diana Gale Matthiesen):

29	26	Roberts James	37	M	W	Farmer	2500	300	Michigan
		_______ Kate	32	F	W	Keeping House			Massachusetts
		_______ Frank	12	M	W	At School			Iowa
	27	Roberts John	40	M	W	Farmer	400	300	Michigan
		_______ Sarah A	32	F	W	At Home			New York
		_______ Jessie	3	F	W	"   "			Michigan

James ROBERTS/ROBARDS is John's brother.  Based on earlier censuses, John should be 41 years of age.

5.  1880 Census Every-Name-Index/Images (online at Ancestry.com, Image #14 of 42):  Litchfield, Hillsdale Co., MI, Roll T9-0581, p. 184B, PN 14, SD 1, ED 88, enumerated 25 Jun 1880, official enumeration date 1 Jun 1880 (extracted by Diana Gale Matthiesen):

1880:  for an explanation of the column headings, please see What the Numbers in the Federal Census Mean (missing columns contained no data).

1

2

3

4

5

6

8

9

10

13

14

21

24

25

26

361

396

Robards John M

W

M

48

/

Works on railroad track

2

MI

NY

NY

_______ Sarah A

W

F

43

Wife

/

Keeping House

NY

NY

NY

_______ Jessie T

W

F

14

Dau

/

At School

/

MI

MI

NY

_______ Don? J

W

M

9

Son

/

/

MI

MI

NY

John's middle initial is clearly "M," and he is indexed "John M."  Based on earlier censuses, John should be 51 years of age.

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

7.  Messages in the Robards Family Genealogy Forum (online at GenForum.com).  One message includes an excerpt on the ROBARDS family from the following source:

7a.  Vivian Lyon Moore.  1933.  Lineages of Some Early Hillsdale County Families.  Typescript MS.  Gives John's middle initial as "M" and his birthyear as 1832.