I don't know where you live, but you need to check the gun laws in your state. Here in Massachusetts, you cannot purchase any bb, pellet or paint gun unless you are 18 and you cannot have one in your possession in a public place under the age of 18 without an adult present OR unless you have a sporting or hunting license. They won't arrest you in MA for violations, but confiscation and fines are statuatory and if you are found using them for vandalizing, the police have the right to arrest you. Laws vary from state to state. You can find the current laws for your state by doing a search on the web.
That being said, I guess my first question would be why does your son want one? Is this something he has wanted for awhile or a recent request? Does he have an interest in hunting or is he planning on torturing the squirrels in the neighborhood? Is your husband into hunting and do you already own guns? If not, regardless of what the law requires, before you buy a 17 year old ANY type of weapon, be it bb, pellet, paintball, whatever, you need to send him and yourselves through a safety course so that you understand how to handle guns, period, and that they are not toys.
But please make sure you are within the laws of your state before making a purchase of any type of weapon. And please make sure you are ALL trained in safety before allowing any type of weapon in your home.