AS long as the engine stays within the parameters of leakdown, oil consumption, oil analysis, filter cut etc.. I had a twin of which the engines were factory new in 1975 had 1400 hrs on them in 2005 and didn't use a drop of oil and had absolutely no leaks. Compressions all 70's/80. Its the components that you must look at especially the mags and FCU's, lines, hoses etc. Personally i don't go much on the chronological age of the engines but the condition and maintenance is very important. I often liken aircraft engines to taxis....some can be only twelve months old but have done a million k's. Don't agree with the 12 yr life for chtr also.