I would start the "training" for this project immediately!! Even with small kids, you should be able to steal away for a weekend or two to train and then, once a year try a section of the trail for a week.

Better start now, and you'll be fit as a fiddle and ready to go the distance when those kids hit college age. They can drop you off and pick you up when they have their licence, you'll be near enough to retirement so you can take the time off!
Listen to the trees in the wind