take off shoes and use toes if you have to

Recent read:
Author stated that hero was 25 and had joined the military 9 years previously.
This would make hero 16 at time of enlistment, perhaps if this had been an historical I might have bought this. But it was a contemporary and later we learn he would have been at least 17, most likely 18.
Why, oh why, is something as simple as basic addition so elusive?