Roy is now 5 months, 50 pounds, 21 inches tall. At what age will a boxer reach full mature height? He appears not to be growing upward anymore. On another note, what is the maximum amount of exercise for boxers. We walk if not every day, every other day, a minimum of two miles up to 5 miles in one stretch. He shows no exhaustion, dehydration, abnomal bowel movements or stress.