Age & fitness count huge. You could probably leave today, doing 120km/day for first three tour days and be fine, with only maybe a little soreness. By the fourth tour day you can open up

If you have time & desire to train I'd recommend working up to doing back-to-back days of 80km/day. When you feel great after doing back-to-backs your ready to go.

No matter what you'll achieve a zen-like-oneness with your bicycle after two weeks on the road.