Walks themselves aren't bad - but you just need to ensure that they're of appropriate duration, is all. And a good rule of thumb is 5 minutes for every month of age over one month - which means that a 2 month old pup can go for five minute walks, a 3 month old for ten minutes, and so on.
Bear in mind that walks for puppies are all about socialisation and learning to walk on a leash. The pup's exercise needs should be met solely by playing and offleash running. But sometimes the appropriate walk time isn't enough for the socialisation purpose - in which case, it's worth remembering that there are no rules that say you can't pick them up and carry!
Offleash, where the pup can run and stop and rest and pause and run ahead some more - it's fine for "walks" to go on longer. It's really just the "forced exercise" types - which includes leash walking, or any situation where the puppy is going to try to keep up with or outpace you rather than pause - that need to be time limited. There are some good suggestions for socialisation experiences for your pup at
www.boxerworld.com/puppy/socialisation