When sending nudes, which has the potential to backfire, it should really be down to your own judgement and what you enjoy and are comfortable with; not what other people do or what is seen as normal.
To give it my two cents, I've never sent or recieved explicit pictures, and I've been in relationships both with other 22-year-olds and people similarly younger as yourself. It's not a *normal* stage, but it's also not uncommon for couples to do, so it really is just down to what you want. However, if the other signs of a real friendship/relationship aren't there, and sending nudes is your way of keeping the relationship going, I'd advise you that your inexperience is probably being taken advantage of.
Don't worry about the law, the police are very unlikely to care as long as it's all consensual, even if they did somehow find out.