Hip/groin flexibility

I'm a late comer to the sport (TKD), having started at age 36, nearly 3 years ago. My flexibility has steadily increased since then, but I still struggle with hip/groin flexibility. The stretches we do in class don't seem to reach the right muscles/tendons. Of course, it doesn't seem to effect my younger classmates who pivot and jump at the bags like mini helicopters...

Anyone have some great hip/groin stretch routines they can share?