497's boiler was built in 1902 making it 99 years old this year.
Before it got set aside by managerial stupidity and expiring tube time (don't get me started on that!) in Jan 2000, The Fort Worth & Western's x-SP 2248 was going strong at 104 (blt in 1896). At the time, I think she was the oldest regularly operated SG locomotive in the US (complete with original lap seam wagon top boiler!)
Recently (like last weekend) the Texas State RR celebrated the 100th birthday of TSRR 201 (x- Texas Pacific #316).