How old are most of the reinforcements replenishing the Second Company?

The reinforcements are a few years younger than our main characters.... seventeen to eighteen years old.

Reinforcements have arrived. The vacancies have been filled and the sacks of straw in the huts are already booked. Some of them are old hands, but there are twenty-five men of a later draught from the base. They are about two years younger than us. Kropp nudges me: "Seen the infants?"