Its never too old. :D but i am a little bit confused, you want him to go inside? (or he's an indoor dog, and he should go outside.. prolly that..) anyways, being a puppy still, i would take him out after playing, after waking up, and a little bit after eating. at 6mos, he probably won't have to go as much as a 8wk old, but still watch him. And when you take him out, u may want to put him on a lead, and take him to a designated spot, and make sure he goes. then praise him like crazy after he does his business!

good luck! welcome to the forum, and congrats on the new edition! Can't wait to see pictures!
-Kat