Damn...first off, I ought to say thank you for letting me live the MILF dream vicariously. I'll be 25 soon, so I've still got some time, but the clock is ticking down to the moment when they stop being MILFs and start being peers.
The best advice has already been given. You need to strike while the MILF's hot. She might be obsessed, but whats the worst that could happen? And let's face it: if a 40-year-old woman is chasing a 21-year-old cousin of her friend, she might be after the same thing you're after - she may just want to hit it and quit it.
Also, pics would probably help us give better advice.