5 is the right age to start (I think that's G-Jugend) and now is a good time to start as they are just emerging from the indoor season to play outside again.
By the time they get to 7 the Germans have sorted out who they want to keep in their squads and mostly told the other boys they have no chance (in a way only Germans can but the equivalent of "F&%$ off you're useless!"). It's awful but that's the way a lot of clubs are run. 1860 Munich scouted and took a boy from my sons team when the boy was 6...
Unterhaching takes boys all the time and Bayern take the cream of the crop. Most get chucked out again a few years later.
There are clubs all over Munich and the sourrounding area. If your son is in a local school then ask the other parents where their boys play football and go there as he'll at least know some faces.