Welcome to the board!
definitely no biking for another 1.5 year. Remember that while you pup has tons of energy, they are still very much growing. You want to avoid any hard impact exercise until joints are done growing (18-24 months). hard impact/"forced" exercise is lots of repetitive impact on hard surface. Even leashed walks should be limited to a certain extent (5 mins per month of age) but definately avoid any running, biking or roller blading until dog is done growing. So 4 walks of 20 minutes is good for leashed stuff.
NEW APPROPRIATE EXERCISE
Having said that - you want to encourage off leash free play on soft surfaces. That they can moderate on their own with lots of start-stop and rests. If you do not have a yard, use a long line and a harness. Stuff like fetching. walks are great but on leash walks don't tire out a young dog. This is the key to a tired puppy, this offleash running and playing. Do play dates with other dogs.
The other important thing is MENTAL exercise. work that little brain of theirs. Lots of short training sessions. Don't use food bowls, meals should be worked for (use stuff like kongs, food toys, food games, training, there are some you can buy and some you can make at home).
and lastly - once they have had sufficient physical and mental exercise, they need ot learn to chill. otherwise they can become energy junkies that always need to be entertained and need more and more and more exercise.