I'd say he's already sorta "training you" that when he barks, you should pick him up, so, I'd be nervous about letting it go any longer like that. He should be old enough to teach him to sit right now. It's a very easy command. Finn was eight weeks old and it took only a few training sessions and he was sitting with just a hand signal. But, I don't know, I'm not a behaviorist or trainer, just have read a lot on the topic. But, I'd say not to wait til he's older, but, I'm also really rigid with my own pets about knowing their place. I don't let my dog on the furniture at all, I don't let him go out of doors before me, he eats after I do, etc. So, I guess it just depends on what you're wanting from your pet.