Dennis, I think it sort of depends on where you are and how much humidity you have. I presume that this is wood trim on a masonry home??? One reason it is peeling might be that the builder didn't prime the wood properly and just slapped a coat of paint on the bare wood. It probably would benefit from being scraped down to bare wood, then a coat of a good oil-based primer (which can be tinted to your color coat--or close to it) before putting your color coat on it.
I'm no finishing expert, so you can probably assume that some of the experts will chime in, but this is my initial reaction to your problem.