Puppies like babies tend to sleep a lot as they have a lot of growing to do! How much they sleep ultimately depends on how old they are. Young pups still nursing pretty much sleep 90 percent of the time and the rest is spent nursing and crawling. At around 4 weeks pups start getting more active and you may therefore watch them start playing too. As they grow, they'll do several play sessions, then their batteries seem to discharge and so do a big nap and then back to playing. A 12-week old pup can be awake a lot longer than an 8-week old pup, so yes, age is a factor.
Make sure your puppy has opportunities to sleep during the day. Some puppies need some help to fall asleep soundly. Create a quiet environment and remove stimulation for a while. Covering the crate with a blanket can help. A tired puppy can turn cranky, so if your puppy is misbehaving a lot, it could be he's just super tired and in need of a nap.