Yes, 5 years isn't quite old enough for the wood to be degraded. It could very well be termites, or it could be a species of ant that eats wood (carpenter). I had that problem in my house (luckily not in my deck). I did call Terminix to treat the house. Not sure if they would treat a deck as well or what the cost would be. It would certainly be cheaper to treat that than a whole house though. The shavings are a bad sign, however, so you should call someone in to take a look at it! Good luck!