I'm 19 and still going~<3
as long as you know the right times for play, for work, and for family, then it's all ok to have Tama's as long as you want. The funny thing is, I'm in college and my Tama comes in handy, like in Art. If there is a time limit, I leave my Tama on pause and mute, and put on the time screen. As long as I'm not acively playing, it's alright.
Besides, I enjoy them more now that I'm lder and I know that replacing the battery is possible XD
I think he older you are, the better they get.