Here's some of the boxers I've had:
Apollo Creed at 6 months (crossed the Rainbow Bridge in August)
Guns of Navarone aka "Gunner"
They have TONS of energy, chasing Apollo around the backyard helped me lose about 50 lbs in 6 months.
Apollo was full-throttle outdoors and indoors for like 23 hours a day. Gunner is considerably more calm inside the house, but I attribute that to him having a playmate in our Rottweiler puppy, Kaiser. They both start puppy obedience training in January, after they are done with their initial vaccinations.