I can't promise contortion level flexibility, but you can become very flexible still. I'm still gaining flexibility every time I stretch and I'm 34. Start with the basic stretches---pike, butterfly, straddle, hurdler/attitude, frog, cobra, basket, any others you may know and then add in some of these for a better stretch.
Here are some stretches to help you work on your splits/flexibility. (The pics are me and were taken 4-24-12)
I do not suggest trying to do an over-split until you can do the splits. That would be like doing an aerial before you learned to do a cartwheel. Try not to bounce when stretching, try to keep your back straight and lean into the stretch nice and slow. You don’t want to rush a stretch, you may injury yourself and it’s not as beneficial in the long run. Do not have someone push you down into them, you may get injured.
For the straddle--lay on your back with your butt against the wall. Extend your legs up the wall and then let them fall into the straddle stretch gravity will help pull your legs down (you can also pull down on them to get them farther. Hold as long as you can. Repeat a few times. Also when you are doing your normal stretching in the straddle position, right before you are done stretching, lean forward into the middle and then try to pull through the stretch. http://www.youtube.com/watch?v=-MhiIL6Aojo&playnext=1&list=PL796002DA6BCB9B15
(watch around the 15 sec mark for what I’m referring to)
Another one for the straddle is to sit on your butt facing the wall and try to get as close as you can to the wall and still be in the straddle position.
For the other splits--lay on your back, bring a leg into your chest, hold a few seconds, then extend it. Grab your leg and try to pull it as close to you as you can and hold it, repeat a couple of times bending the knee and extending it. On the last extend, while holding your leg, roll over into the splits. Repeat on your other leg.
These are partner and/or solo---stand against a wall, lift your leg, have your friend lift it as high as they can. And hold it as long as you can. Both knees should be straight. The goal is to touch the wall with your foot. Repeat with your other leg. Also remember to pull it to the side for a heel stretch.
Next lay on your back on the ground and have your friend push your extended leg towards the ground. Same idea as the stretch above, but it works the muscles in a slightly different way since you are in a different position.
Another stretch which will help your splits (and your arabesque penchee). You will need to find a blank spot on a wall and grab a chair. Now facing away from the wall and holding onto the chair for support, take a leg and slide it up the wall like you are going into splits. Hold it for as long as possible then switch legs. Try to keep your legs straight. As you work the stretch move the chair closer to the wall until you are touching the wall in a vertical split.
Next move into a doorway and work one leg up or down the frame depending on what you are trying to stretch. I just tried a few doorway stretches for the first time and I was able to put my foot against the door frame and got a completely vertical split in the needle (6’ oclock) position. This link is so you can see what position I’m talking about. http://kittyscott.shutterfly.com/17055#17054
Another that helped me was to stand up and bend over like you were doing a standing pike stretch, then choose a leg and swing it up vertically as far as you can 7 times and on the eighth time hold the leg as high as you can (you will be in the needle or 6 o’clock position at this point) and then when you let the leg down try to get into the splits. Then repeat with the other leg.
As long as you don’t rush and push yourself too fast, you can really make progress fast. Make sure that you really work both sides as evenly as you can. Don’t lose faith, I’m in my 30s and only got my left splits recently and they could still be cleaner, it just takes time and you can do it. http://kittyscott.shutterfly.com/17055#17053
For a heel stretch or to do a pretty leg hold turn you need to be able to put your chest to your legs in the pike position. The closer you can get your body the better it will look.
From National Geographic channel info on contortion http://www.youtube.com/watch?v=6LiWP6plFno