Young is a relative term. At twenty today (in the closeted world in which we bring up children and teenagers) a person is basically very young. However, at twenty in 1800 a woman would be considered fully and completely adult. It would not be unusual for a woman to be married, running a home and have 2 or three children to bring up. If you were from a lower middle-class family you may at 16 or 17 have been farmed out as a governess. If you poor you would be put to work at 11 or 12.

For the men, in the regular army an Ensign would typically join up at 14. So by 24 you could be a seasoned veteran of 10 years experience! (There were soldiers as young as 12 at the battle of Waterloo)
The men would work if poor from 11 or 12 in factories, mines and as apprentices to tradesmen and if from the middle classes as articled clerks to the professions.