I have the same problem. I am a 36 year old male. Recently, about a month ago, I've developed darkish rings under both of my eyes. I look 10 years older. Before this I looked very youthful and could pass for someone in their late 20's. I am otherwise healthy. I also work out 4 times a week and am in good shape. I've started to increase my water intake as well as cut down on salt. I'm trying anti-aging cream my mother had around in her house. I also started applying tea bags under my eyes and I ordered Elite Serum cream which has gotten great reviews. I don't think this is an aging issue. Pictures as little as 4 months ago do not show this problem. I don't know what to do. I hope the things I've been doing have some effect.
One thing to note is I have been going to sleep very late at around 2 or 3 in the morning, but I do get 8 hours of sleep per night.