My 1974 Grumman AA1B still has the original engine (lycoming O 235 C1C) with 2230 hrs. In 2006 we decided to address the generally low compressions with 4 new cylinders. With the cylinders off we had a good look at the cam shaft lobes and lifters and found them in excellent condition. I see no reason we will not get at least another 10 years and 500-600 hrs out of this engine
Regular use and good maintenance is what will determine how long your engine will last, not an arbitrary calendar interval imposed by the manufacturer to get you to buy one of his overhauled/reman/new engines.