There are lots of different jobs to be done, so if you get too sore bending down to dig in the dirt, you can stand up and operate the sifters instead. Pottery washing is done by young and old alike and it is a great time to sit and socialize with everyone. I guess the only requirement would be that you can't be afraid to get dirty. It is fun to look in the mirror after a hard day at the dig and see just how dirty your face can get. Dust gets everywhere, even in your ears and nose.
Archaeology is fun, interesting and challenging.
I hope I will be fortunate enough to go on a dig again soon.