How to explain the forced conscription into the Ukrainian armed forces?
Ukraine didn't even start a lot of conscription until late last summer because they had sufficient volunteers. That also accounts for the higher average age: many of the original volunteers joined the army in 2014 after the last invasion. Now they've lowered the draft age from 27 to 23 to increase the manpower pool and allow more troop rotations off the battlefield.
In WWII, even the US Marine Corps had to resort to getting conscripts for the Pacific War.