Untreated aged pine should be OK, but you need to know for sure it wasn't pressure treated, and I gather fresh pitch in the wood can be an irritant as well as messy.
Yep, I think the treated pine is darker and perhaps smells odd, fresh, untreated pine is pale and smells good. I think the treated pine is for outdoor use only, indoors you use untreated wood. I buy large pieces of pine at the lumberyard and give to my birds, it´s cheap and they love it.