Hi avm228,
I have only found the 4 documents associated with his discharge which I have transcribed and analysed in some detail. The point you make is a good one and I had already made some calculations along the following lines. If his age at discharge (39yr 8mo) is correct, and we assume it was exactly 8 months with no fewer or extra days, I calculate that this gives his birthdate as 28 September 1824. If we now take this date and compare that with the date of enlistment (14 September 1838), he was 13yr 11.42mo. But if he did join on his 14th birthday as you suggest, with 30 days in September, he should have been born on the 17th day of September. Tell me if this is just counting the same thing from two ends or is it valid - my date arithmetic never was that good and Excel does make it just that little bit easier to make mistakes faster.
Even if the above does work, and lets say the day and month are correct, we still have the problem of different birth years being suggested by other documents:
1871 census in Hereford at 43 - birth year would be 1828
Death certificate in January 1900 at 73 - birth year would be 1826
And of course, still the final problem of finding documentary evidence for all this.