Getting better flexibility takes time and slow, diligent work. There are some good books, tapes out there. Century and Barnes & Noble are usually where I go to for references. Jean Frenette's Guide to Stretching paperback. "Stretching Scientifically" is a good tape or book.
Women usually have better flexibility. But some men and women don't because they don't work on it, occasional isn't enough. I usually do some static before class, dynamic during class and isometric/split work after class. Three types of stretching, static-stretching slowly and holding it for 20 sec., dynamic - fast - starting low and progressing to a high stretch front kick (not the same as a striking front kick-toes not brought back, then isometric, where in splits while you hold the stretch, you tense the inner thigh muscles for 20-30 sec. and release. Its good to stretch every morning. Its better to do some warm-up like jumping jacks or my favorite, just jogging for 5 min., then I start the static.
You are gradually building the strength of the opposing muscles. When you stretch one leg the other lengthens, gets stronger. But NEVER bounce, I tore my hamstring doing that as a blue belt and it took a year to really heal especially while continuing to work out.
I started out not terribly flexible, but now can do a full up front kick and a head level double side kick and a near split - an inch or so more! After 7+ years. So the key is to keep working on it and do it slowly. I stretch until uncomfortable not to pain, in sets and slowly you loosen up.
Hope this helps - and its good to read - check out books!
