Steam engines are like aircraft and other machines, they will last forever, given proper maintenance and funds for care. The problem is as Mick stated, here in the east main line steam is pretty much a thing of the past, the class ones had a bill passed in the state house for a minimum of 200 mil insurance to run on their railroads. It killed everyone, after years of fighting it was repealed two years ago but I doubt we will ever run again. If you dont have your rails your out of the game. The UP is about the only place you can see big steam but friends it only takes a change at the top to pou a end to it all, aka NS. Glad you have gotten into steam, its still pretty much a on the job learning curve, as in the past, as it should be! Look into joining the Friends of the C&TS.
Charlie