Frequent bathing for any dog is unhealthy as it deplenishes the natural oils in the skin. If your puppy is getting dirty from playing outside you may just want to brush him, but if you aren't using any soap at all, it should really not have any affect to rinse him off if he is a normal, healthy boxer.
Bella will be one year old on the 7th of October and I have never given her a bath yet.
Boxers are naturally clean dogs and will groom themselves much like a cat will.
Bella's been swimming in the summer months, so I "kinda" count that as a bath, but an actual bath with soap and water, no, not yet. I would if she got extremely dirty, but even on rainy days when her paws get really muddy I just towel down her paws and legs and when the mud dries, give her a good brushing.
I'm kind of old school on the "bathing" thing, and really think that once every six months is frequent enough for a pooch that doesn't get to go swimming.
It depends on what your standard of "dirty" is I guess! If Bella were caked in mud I would give her a bath, but just normal backyard dirt, no, I brush her or towel her off.