Fatal accidents due to mechanical engine failure have averaged about 2.5 per month in the past 16 years. Probably not, but we do not have good data on the age of the particular engines that failed. The NTSB does not collect that. The manufacturers do not release data on the mean time between failures. While we are always concerned about mechanical problems, it remains the smallest part of the accident picture.
Pilots are still by far the most likely component to fail.
Parking an aircraft outside instead of in a hangar increases the aging process. Not necessarily, but it will increase expenses and it puts the burden on the owner to invest appropriately. Pay hangar rent or pay for more maintenance this seems to be one of the axioms of ownership. Paint fails more quickly when subjected to the sun, and when that happens the aircraft skin begins to corrode. Water invariably finds its way into some inaccessible crevices, and again corrosion potential increases.