Get a bicycle asap, and start riding. If you can get ahold of a bicycle this week ... and it doesn't have to be anything really special ... by next weekend, you could be out doing some 5-10 km rides.
By the September long weekend, you could do a short tour ... cycle 30-40 km to a campground on Saturday, do a day ride around that area on Sunday, cycle 30-40 km home on Monday.
When you turn 50 in October do another weekend tour to celebrate.
If you enjoy doing that sort of thing ... keep it up through the winter and come next June, you could be on your way across your country.