Fixed gear for people over forty?

Thinking of getting back into fixed gear riding after getting rid this year. I thought it had caused my plantar fasciitis...it didn't (well, I'm pretty sure).

So what sort of age can people ride fixed gear in hills or on audax's?

If your over forty and suffered from fixed gear related aches and pains let me know...cheers.

I am 65 this year and just returned from a 500 mile return fixed wheel cycle ride to visit family! So age is no barrier. Just ride and enjoyed.