That is very interesting. Parker's eldest brother Thomas had served for three years in the Life Guards (which was obviously far more expensive in every way than a line regiment of foot like the 76th), yet when Robert Parker indicated that he wished to abandon his position as a clerk in articles to an attorney, Thomas told him that, ‘I consider a younger son has not any business in that profession except he has a tolerable fortune to support it with … [and without it] he had better return to the Profession he as wished perhaps hastily to leave.’ (Thomas Parker to his mother Elizabeth, 15 July 1808, quoted in French & Rothery Man’s Estate p 120).
This a subject on which I have been doing a good deal of research in the last couple of years - I'm writing a book on the position of younger sons of good families, their need for a career (because they didn't inherit much, with the estate generally going to their eldest brother) and the limited options they had: the army, the Navy, the Church, the Law and a few others, and the prospects they faced in each of these careers.
But I didn't expect that poor old Robert Parker would be such a perfect example.