The idea of leaving the trainer flyable as long as possible is a good one.

Some peopkle get lucky... and thier original trainer survives 20 to 30 years, being flown regularly.

The average trainers don't survive much past 6 months. Part of this is of course due to people trying to teach themselves and those trainers often survive just under 5 min at the airfield. If it survive the first 5 min of flying... the probablility it will suvive more than a month goes up dramaticly.