A steel frame has no "use by" date to it... It can be overloaded to the point of fatigue, but will usually show signs of it; cracks, bulges, etc. If inspected regularly, and taken care of, it will last a LONG time. I do have a steel frame damaged from being overloaded (not by me). This one was used as a fully loaded tourer by a heavy rider... and lasted for many years and many thousand miles before starting to crack behind the lower head lug. It was still being used by the previous owner, and he didn't even know it had a crack. I bought the frame from him, and he refunded my $$ when I convinced him the frame was no longer safe... I kept the fork, which still looks perfect (Reynolds 531/Campagnolo drops).