The only clues to John Ham's birth are that he was 40 on death in 1846 and that he was 35 in the 1841 Census. The age at death being a multiple of 10 might indicate that it was a guess while ages in the 1841 Census were generally rounded down to the lower quinquennial age.

I have not found a baptism entry that I can be confident with. Also the surname Ham often gets transribed incorrectly e.g. as Hann, Harn, Hamm.