I don't do PSA, but I have looked into it. It sounds like you are talking about the PSA PCD title, the entry level title something like a BH. I checked the rule book quickly and didn't see anything about the age of the dog when they are able to compete. You wouldn't need to pass that to start training. In any case, I would start training my dog as soon as possible. If you have trials near you, you can check to see who is organizing them and see if you can go to some of their practice sessions, that way you can see what they are doing with the puppies.
My husband and I have a Malinois that does French ring and we have taken him to a couple of PSA training sessions and we saw that it could cause some problems with French ring, so I would think it could be the same with Schutzhund. There is another Malinois that is currently doing both French ring and Schutzhund, so it it possible to do more than one sport, you just have to really know what you are doing.
Jeanne -- Milo and Akasha GSDs
Halligan and Axe Malinois
Waiting at the bridge: Nikki -- GSD, Duchess and Battle -- Malinois