1825 Royal Artillery attestation Cupar Fifeshire

[Westee]

My ancestor who attested to the Royal Artillery in 1825, said he was 18 yrs old.  But the only birth details I have for him state he was born in 1804. 
It would be unusual to state you are younger than your real age.
I know that during WW1 and WW11 the men did raise their age in order to join with the army.  But I have never seen someone saying they were younger than they were.  It was, however, 1825.  Maybe he didn't know his real date of birth.  Any suggestions.

[ShaunJ]

Perhaps he wasn't quite tall enough to meet the minimum height requirement for new recruits (5'7" at that time I think) and was squeezed in on the basis that he was only 18 and would grow.

[Westee]

How interesting; thank you so much.

[GR2]

Are you certain that the details for his birth are correct?

[Westee]

I have the OPR's for Dysart and that is what I am going by.  There is another family there with same name for which I cannot find one church or baptism record; only the marriage.  Has annoyed me for years that I cannot find a closer date or baptism record.  So am just going by the one I have.

[Neale1961]

I have the OPR's for Dysart and that is what I am going by.

That will be date of baptism, not a date of birth (unless that is specifically noted.)
Perhaps he was baptised as a child, not as a newborn.