Originally Posted by big john

I'm 68, been riding off road bicycles for 30+ years and off road motorcycles for 10 years before that. I think it's great fun and has the advantage of no cars. Also, wind and weather is much less a factor than on the road.

If you're going to try it, start easy and get used to the feeling of the bike moving around. You can't just ride like a road bike, you need to learn the techniques and practice. If you're riding dirt roads and smooth trails, any bike will work. If you want to do anything technical or ride with any speed, I recommend a full suspension bike.

A rear suspension is easier on your back, will track the ground better, and will save you from your mistakes. Also, the rear brake works better with suspension.
I have what is known as an "enduro" style bike. 160mm fork with 150mm rear travel. It's 32 pounds and a bit of a chore to climb long hills with, but it's so much fun to descend on. If I could just get a new bike now I would go for a shorter (120-130mm travel) lighter bike. I've tried to tone down the risk in the last couple years and I have no problem getting off and walking a section.

No form of bicycling is completely safe but my worst crash was on the road bike on a bike path.

Here is my KHS.