Same age... this thread is really making me feel old. Generally I still feel like I'm just getting out here and just getting started still in terms of career, life, etc. I really hope it's not all downhill from 30!

Related to the main subject, I don't think my levels have ever been low, but I've always been surprised at how quickly I lose muscle mass when I'm not working out. That might be more related to protein intake and other genetic factors though, since I've always been pretty lean.