I'm just going to plug the link in my sig, here ...
It's a simplified version of the "just spend EXP on what you want" character creation method, using the skill categories in the AToW book which are based on occupations. So if you wanted to do what you're describing here, you could just buy the infantry skill category at a higher level.
Meanwhile, if you like you can still go through the life paths system, and choose traits or individual skills to represent the most important things you learned in each phase. You just get to bypass the whole "This phase gives you 50 EXP towards Illiterate" and then add it all up at the end, thing, and all the other bookkeeping AToW makes you do in order to make life paths approximate point-buy.