I'm 38 years old, had OA in my right hip from a childhood accident, and had a THR of my right hip in September of 08 (I was 37). I have to run for work (both sprint and distance), so I couldn't hold off until the pain was completely debilitating.  I was in constant pain and was very worried I'd never be able to perform my job fully again.

I had a fantastic doctor who gave me no limitations/restrictions, I just had to listen to my hip. I started C25K in May, and have done 2 5K's, with more on the way!  I think running has actually made my bone and muscles stronger, and what was left of my "gimp" is completely gone now.

One major thing I did was learn the POSE method of running.  I don't heel-strike anymore, and in addition to not having any hip problems, I have no shin splints or any other running issues I've had in the past. I think one of the reasons running is considered a "no-no" after THR is because of the jarring from heel striking.   Disclaimer: I'm very biased towards POSE, since it really opened the world of running for me. I'm not knowlegdeable about other running techniques, and I'm sure more experienced people can give you better insight about running form to reduce jarring impact.

My hip gets cranky every now and then when I push too hard, but the surgery is well worth it!  I wish I hadn't waited as long as I did.  I was in pain for years.

Best of luck--if you need any more info, please don't hesitate to ask!

MsC