Well - scotlandspeople records have been useful! It's very clear the John Bishop born to William Bishop and Helen Maxwell in 1809 is not our one since there's a death record showing he died aged 10 weeks. Same parish and father, a chimney sweep, in both baptism and death records. Rather unfortunate since I don't have more than a guess as to his actual parents!
Firstly his age : told the army (in 1928 and 1852 - consistent!) he was 20 in 1829 hence the 1809 birth year. However the 1871 Census Record which is clearly his indicates 1812 as does his apparent death record. I have no good idea why he'd lie to the recruiting people - doesn't seem there was much of a minimum age requirement - but I'm very inclined to think 1812 is right. Perhaps he thought he'd be an initially perceived as a bit more senior than a 17 year old?
My 1812 assertion is supported by there not appearing to be any 1809 baptised alternatives. I've discarded any 1814 baptisees - can't see a 15yo claiming to be 20!?!? Re 1812 Johns - it's not son of John B & Jane Henderson's as asserted by you, Monica, above. All I'm left with is son of George Bishop & Hellen Linton, born 26 Jan 1812 at Portabello, baptised Edinburgh St James Place Relief on 16 Feb 1812. (They had another son, George, same place in 1817.) This, however, is a purely name and place on a single document based - notoriously unreliable!
But wait, there's more : there's a baptism record on 4 Mar 1832 at Oldham, Lancashire of a Christiana daughter of Christiana and one John Bishop "soldier in the 91st Regm of Foot".
https://www.familysearch.org/ark:/61903/3:1:939J-4LVL-Q?i=397 Can't be anyone other than "our John"! So, now we have :
- Christiana b 1832 in Lancashire mother "Christiana",
- George Manson b 1837 at Dingwall, Scotland mother "Catherine Shanon",
- William b 1839 d 1840 at Jamestown, St Helena mother "Catherine",
- James McKay b Oct 1841 at St Helena, bap Dec 1841 at Cape Town mother "Catherine",
- Elizabeth Anna b 1844 at Fort Beaufort, Eastern Cape mother "Christiana" (remember her?), and,
- Living in 1871 at Burton-Bradstock, Dorset with "Ann(e?)".
Bigamist? Philanderer? Unlucky widower? Husband of lady using different names at different times?
Have to say old John is giving me the proverbial pain in the posterior!