I'm 45 in a month and can agree with a lot of what is said above. I'm coming up to 30 year on a mtb and like Vik live somewhere I can ride all year round with trails reasonly close to home. In addition my commute to the office involves a little offroad (or a lot if I take the scenic route).
Another key to riding all year round has been night riding which helps keep the skills and and fitness up over winter.
Here's hoping to still be riding at 80!!!