Is it illegal for a 22 year old to date a 16 year old?

I'd have to know more to answer this question. Are you the 22 year old or the 16 year old? And what do you mean by "date"? If a 22 year old in the US is contacting a 16 year old in Europe, and having relationship-type conversations, and sending sexual photos back and forth, the 22 year old in the US may indeed be charged with Child pornography charges and other charges and end out spending 10 or more years in prison and being labeled as a sexual predator for life. Anyone in the US who is over age 18 who wants to carry on any sort of relationship with anyone under age 18 who is anywhere in the world, should first bring the details to a lawyer and get advice. Better yet, if you are over 18, carry on relations only with people who are also over 18 years old.

It is not illegal to date someone 6 years older than yours, although that's pretty difficult to do from a distance as dating usually means spending time together. However, several relationship behaviors may be illegal such as sending nude or suggestive photos to each other online.

Without a physical relationship, there are no laws broken. As long as the relationship remains in the form of electronic communication (and no compromising images or videos of underage individuals are shared), you should be fine.