http://anysoldier.com/
If you click on WHERE TO SEND, you will get the info you need.
You can also seperate by branch of service too.
You can also search by ranks once you get to the page of the service....check the ranks...ie SFC, SGT, CPL, you can sort of get a general idea of their ages.
PVT, PFC, SPC, CPL, SGT 1LT, 2LT, ENS, SN, FM, and any that have just 4 letters (Any 2 letters together with a number after it,,,such as MM3) are mainly probably no more than about 25. So if you are wanting to "target" the younger ones. (PVT, PFC, SN, FM and anything with 2 letters and the number 3 will be the mainly the youngest)
If you live near a military base, you can call the Base Liason and ask about donations also.
Just thought I'd add my 2 cents