Hi Katherine,
Welcome to the site. I am a tonsil cancer survivor myself so folks with more specific ideas about tomgue cancer will respond to you.

If at all possible, I would seek out a comprehensive cancer center for your followups. They do see people your age with oral cancers there (although it is a little unusual for someone your age). That is even more reason to be be very careful. Did you have a PET or PET/CT before they started treatment? How big was the tumor? How did he determine there is "no evidence" of lymph node involvement? What was your staging?

"Watchful Waiting" is what most of have in the way of followup. Just guessing, it sounds like they caught it in a very early stage and a single treatment modality would be fairly predictable. Tongue cancers can be aggressive however and some feel it is better to hit them hard right away. If you can't get to or find a comprehensive cancer center in your area, at least get copies of your medical records and scans (they can put them on a CDR) and send them to one for review just to be on the safe side.