There's usually places with single track that isn't very technical that would still be fun.

I know gunnar makes steel mountain bikes.Surly's got the instigator or the karate monkey,things like that... Rawlands has a steel frame that can be built up as a mountain bike, but I think the top tube is going to be too long.

Given the suspension that is on mountain bikes - I don't think it's really necessary to have a steel one instead of an aluminum. If you're planning on riding rigid than it makes more of a difference.

I would just get a hard tail if I was you - it really requires an investment of a lot of cash to get a lightweight full suspension bike - the cheaper ones are heavy, andI don't see the point pedaling a 30+ bike up obstacles. However, maybe a full suspension would be better for your wrists/hands.

Do you have friends that you could borrow their mountain bikes for a bit?

If you want to go further - there's titanium. Litespeed makes nice titanium mountain bikes.

Marin used to make nice steel frame bikes, you could consider picking up a used marin,probably about a 14" frame.