It is a bit like staying out late at night when you were a teenager: didn't you learn that, anything you could do after midnight, you could also do before midnight? Anything you can do under 60 years old, you can do after the age of 60.
Assuming that you obtain the blessing of your physician or other health care professional in advance, there is no reason why you cannot do weight training a couple of times a week as well as stretching and mild cardio (such as brisk walking) every day or nearly every day.
If you have not been exercising, start very slowly. With respect to weight training, learn and use proper exercise technique. Here are two important tips. (1) Warm-up thoroughly. (2) Give yourself extra recovery time.
7 year olds should do 10-16 reps of any exercise
1 hour
1 hour
30 min a day
115
A lab should get an hour to a half hour a day
at least 3 hours
Three fifty should be pretty easy for a 15 year old male. Pump it up buddy and keep on lifting!
120 lb
A ten year old boy should receive up to 120 minute a day of exercise to get the muscle working and growing strong. He should also eat alot of proteins and vegetables as well as meat
7 hours a week, for champions
3600 hours just kidding it is about 3500 seconds witch is 60 minutes witch is 1 hour