Weights the likelihood of command positions by your age.

For most head positions, a good age is between 25 and 60, with ages towards the middle of that being even better. 25 because I figure for stuff like research, engineer etc. they'll want someone with fresh knowledge. Captain's best age starts at 35 though, due to that being an "old geezer job".
Merge pull request #3010 from CIB/feature

Weights the likelihood of command positions by your age.