Well most grown men (including me) can't do the splits, which is probably why you're not getting too many responses. I'll give you advice from a guy that could do them--easilly--at age 50.
Went to a Bill Wallace seminar and it was about 50% a stretching routine. He pointed out thatt the three muscles to loosen up to do the splits were the groin (obviously), hamstrings and hips.
SInce he can go to 180 degrees fairly easily, he did the splits by sitting on the floor and starting in a comfortable split (about 150-160 degrees for him). After about 8 seconds he pushed one foot out and forward a few inches, increasing the split. He'd hold this for about 8 seconds and then repeat, continuing until he couldn't push his foot out any more. Doing this safely allows you to push past a full split position. It's much safer than using chairs and you can use the same principal even if you can't do the full splits yet.
For hamstrings he stood up with the feet confortably apart (not a full split, but maybe 3') and stretched down to each leg, bringing the chest to the thighs and then grabbing behind both ankles and trying to pull your head down towards the ground. He held each stretch for about 5-6 seconds and did it three times to each leg and the middle. (warning--don't do this one in mixed company

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For hips, he did the "frog". This is where you start in a wrestling base and then allow your shins and feet to slide out to the side, so that you're on the inside of your shins. Move your body forward and try to flatten in without raising your feet. Hold for about 10 seconds and then push your body back by moving your body up on your forearms. Hold this for about 10 seconds. Move your legs an inch or two further out and repeat. Repeat one more time.
He suggested doing this entire routine three times while stretching. By the third time you should notice your splits widening, unless you're too sore the first few times. From the way you described it, you might be able to get the rest of the way there doing a routine like this for a month or two.