We recently (about 4 years ago) got rid of a 30yo 75g upgrading to a 125. If the tank hold water, and that can be demonstrated for you if it's currently sitting empty, I'd say go for it. 6 years is not old at all... if tanks were useless after 6 years, I'd be really worried about the state of the hobby. When I was in my early 20's, before I moved out of my parents home, I had many smaller tanks, none less than 10 years old, all perfectly fine. Two of them were "second hand" 55s, each originally belonged to the father of the kid I purchased them from. Both were originally purchased in the mid to late 70s. I left them in the beginning of the 90s, still holding water.