It is all relative to age. If you are a teenager, PLEASE do not go under 2 years for the lub of god. It's just gross. If you are 18, no lower than 16. If you are 16, no lower than 14...even 15 maybe, otherwise it is sketch.
But it changes. It is perfectly acceptable for a 28 year old to date a 21 22 year old. A 30 year old with a 22 year old. Especially if they are working and not in school anymore.
But until you are that age, please...stay away from the youngins.
We'll have you dead pretty soon.