An excellent example of how MF's track will age would be Shockwave at Six Flags Over Texas. This is one of Anton Schwarzkopf's wonderful double-looping creations. I was at the park in the middle of March and this 22 year old ride is still smooth as glass.
On a side note, it's probably no coincidence that Intamin's box track looks so much like Schwarzkopf track. I was just reading yesterday on the Schwarzkopf site that Intamin used to represent Schwarzkopf.