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Climbing? You don't need experience, can exercise together with more experienced people. Your skinny build is an advantage. It can be done indoors and outdoor and will train most of your muscles. You won't get bigger boobs though...
How expensive is climbing?
 
Personally I am a fan of mtn biking. The draw back to it is the entry cost into the sport is around 500 give or take. Reason for this is a good starter bike is a least 400 plus you will need a way to carry water and a helmat. Going cheap with a wallmart bike leads many to quit the sport before they find out if they like it because of the crap bike. If you do like you would want to replace your bike very quickly so you are still out the money.
If you get the better bike and you hate it you can always sell the bike and be out about the same as if you went with the walmart bike. Net loss is the same either way so might as well go with the choice that gives you the best hope.

I like mtn biking because it is something I can do by myself and it is a good work out. Only problem is I really have gotten in to it since I got my bike and have spent a lot of money on equipment like clothing gloves, roof rack and a 300+ on upgrades to my bike that was 500ish new.

I've been avid in street bike myself didn't get an actual drivers license till I was 20 I've done a little off road but I prefer pavement--more speed than terrain either one is good.
 
My suggestion is to run cross country in the fall and run track in the spring. They are both great sports because of the team aspect and everybody is welcome as there are usually multiple races for different levels.
 
Ice hockey.

I used to coach women's ice hockey, and they always need help in practice. It helps younger women develop their strength and skating so that when they get older they can play in college or in rec. leagues for fun.

No checking, just great exercise. Great for coordination, balance, cardio and then all the positive mental aspects as well.

chicks and hockey :D :p

Golf is a good sport to learn for when your older. its something you can play now and when your in your 60s +.
 
How expensive is climbing?

Not really expensive. You need some basic gear. Harness, belaying device ( 8, or grigri) and shoes. But when you start you can use ordinary sport shoes and rent the other stuff. Access to a climbing center is between 5-9 euros here in the NL.

(if you decide to do it outdoors you need more gear, but the entire climbing group can share it. ( rope etc).
 
chicks and hockey :D :p

Golf is a good sport to learn for when your older. its something you can play now and when your in your 60s +.

I used to play against 60 year olds regularly. They weren't as fast as the younger guys, but their shots were on target, and the passes were perfect.

Martina Navratilova was playing hockey just a few years ago, I haven't been in the tournament loop in Colorado for some time so I don't know if she still is. But she's not exactly 25 years old either.

Hockey when played properly can be played for decades. If you're in a testosterone league where you hit people away from the play, because you haven't got the skill to carry the puck in or play intelligent defense, you won't last long. Checking can work at the younger ages, because you're taught how to give and take the hit. But in recreational play, you still have a real job to go to in the morning, so there's no reason to get into stupid hitting plays.
 
Tennis is something that is good now, good for later in life. An advantage to the sport is that outside of lessons, it's relatively inexpensive and it only takes two to play. Also a sport you can play at any age and at any level, anywhere in the world.
 
I have two suggestions... one serious, the other rather cheeky. You can try to guess which is which. :)

1) Ultimate Frisbee
2) Brazilian Jiu-Jitsu
 
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