Simple takedowns should be survivable, but full throws are a different story as gravity doesn't know how old you are. Depending on the technique there are sometimes ways for your partner to let you down easy, but a beginner won't have that ability.
You have to work within your physical limits which shrink with age. You and I have pushed that back further than most folks, but while you can slow aging, you can't stop it. Alternative ways to accomplish goals have to be searched for.
Is there another type of technique besides that particular throw that could be used instead for the combat situation at hand? Or, for example, in a standard hip throw you pivot into the opponent, breaking his balance a bit. From there, instead of teaching a throw that slams you onto the mat, how about a rear elbow at the end of the pivot and follow up with some other cool stuff. At least the student gets practice pivoting into the opponent's space, handles the situation, and you don't get slammed.
There are a lot of effective TMA that don't utilize throwing. Without another body to be thrown, you may have to adjust what you teach. The English alphabet has 26 letters, but we could do fine without a few of them. With 100 techniques in your MA tool bag, there are also some you can manage without. Techniques are cheap and losing/not teaching a few don't drastically affect any art. As you know, it's the foundational principles, movement, and tactics that are the core.
Just go with the flow, old man, and don't worry about it too much. Your student is lucky to have you teach him anything.
