Sounds like everyone already covered most of the important info....Yes the dew claws are usually removed when the tail is docked and a general rule is clipped tail/removed dew claw.....normal tail leave dew claws.....but that is not always the case and generally it is what the owner of the puppies want.
When puppies are born you can actually pinch them off very easy with your fingernail (1 day old)....otherwise like said before it is normally removed with the tails....I have seen boxers with them and without. There is really no difference except that they do need to be watched and trimmed to make sure they are kept short. I actually had a Rott in yesterday that it had grew and curled into the pad and become infected. It was pretty nasty and very sore for the dog.
To me there is really no age on having them done. It is more involved to do it as they are older, but can be done, without any major issues....This kind of depends on the dew claw some of them are tight to the foot and some of them are very loose and hang away....The ones that hang away are more easily removed.
Normally I suggest that at 4 months, if you want to have them removed, to do it when you have him neutered since he would already be asleep...