I used to have similar problems, didn't get them corrected and threw my back out when I was about your age. All the stretching you're doing is good, but the muscles will just go back to square one if you don't get to the source of the problem. If you look into some stuff by Greg Roskoph or Gray Cook, or even the Cressey/Robertson stuff on this site you'll see that flexibility is only half the equation. Cook goes so far to say that stretching is useless if you don't strengthen the opposing muscle.
Getting assessed by a movement professional could be the key. For myself with similar posture issues it was a matter of strengthening my rhomboids and glutes. If you get super-sore traps when rowing and can?t squat too low it might be about the same for you- but I'm not trying to assess here. If you can find a MAT (Muscle Activation Technique) specialist in your area it might be worth your while.
In any case I highly recommend picking up a foam roller and checking out the T-Nation articles on using one.