Depends on how you train, forget age, whats your goal ?
To be healthy ?
To get stronger to faster or go farther, or both ?

The only way to truly build stronger muscles is to tear them down so they rebuild stronger, think 'point of failure' [COLOR=#545454][FONT=arial][B]exercising.
When I finish a ride, after the ride and the next morning I cannot do even one leg squat and my legs are sore I give them TWO days to heal up and during those two days I stretch slowly and not too hard because we should only stretch warm muscles ....
My mountain biking works all of me so the day after a ride I do nothing, the next day I do abs chest and arms.

On my next ride I do Intervals for my endurance on flat trails and ease off on the mean climbs.

My pain killers are orange juice, banana's and water.
My recovery food eaten ASAP after every ride is a cup of rice then a normal meal.

If your not tearing your muscles down your just doing good cardio,,, Its so true, the saying,, 'No Pain No Gain'

Riding every days is fine but to gain power and muscle mass you must ask more of them than they can give and then
give them time to heal to a stronger state..