That is great! Have you read the article "Riding is my Ritalin?" It's from Bicyling Mag. This is the kind of story I love to hear.
My older son (not the former racer) started commuting on our old mountain bike a few years ago. He did it through 2 winters, buying himself a single speed, eventually. We fixed up and gave him our other son's classic Serotta road bike, and he was even thinking of racing at one point. Then he bought a house, a little further out from the city, and was riding home one night with a light that wasn't really good enough. He crashed on a pot hole and hasn't ridden much since then. A few weeks ago, he called me and said he was so stressed at work, he was considering going on meds for his ADD (it's never been an issue since he graduated college). I told him to go ride his bike! He solved most of the problem by quitting his job, as they were giving him no support, and going back to his old company. I am still pushing him to ride more than he does now, given DH's family history with cardiac stuff.
I "prescribe" exercise for anxiety and depression on almost every treatment plan I write. I wish more people would follow the recommendations, but for the ones who do, it really is a life saver.