Studies show that the 4-5 year age gap provides the most stable relationship. Gaps more than 8 to 10 years show higher disillusionment, quarrels and disturbed interpersonal relationships, leading to separation and divorce Bigger age gaps might have worked well for some, but cannot generalise.

Is it OK to date someone 4 years older than you?

Ilmanens answer is correct as far as it goes. If your parents agree with you dating, then it is legal. However, even with your parents and your consent, unless you are married, sexual contact is illegal.

Can a 15-year-old and a 22 year old date?

If dating includes sex (or any form of sexual activity) then the answer is yes - and parental approval is irrelevant. If you are under 16 then you may not lawfully engage in any sexual activity (not just intercourse) with anyone.