It is perfectly fine for a 22 year old to date an 18 year old. The 18 year old is consenting and is of legal age so, there isnt anything wrong.

What is the youngest a 18 year old should date?

This rule states that by dividing your own age by two and then adding seven you can find the socially acceptable minimum age of anyone you want to date. So if youre a 24-year-old, you can feel free to be with anyone who is at least 19 (12 + 7) but not someone who is 18.