Thanks for the link. Am definitely going to have to write for a copy of this person's record, to try and verify that this was the right person.
As for starting up late, my gg-grandfather was born in Dec 1844. Both he and his brother appear to have signed up as soon as (or just before) they came of age. Their father had died in the Mexican War; we believe he was buried in Vera Cruz (one of the majority yellow fever deaths), and their mother died of consumption before they turned 10.
Hard lives.