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.

Can a 21 year old date an 18 year old?

As long as both parties are 18 years of age or older, not being forced, not unconscious, not too drunk to consent, not mentally impaired to the point they cannot consent yes, an 18 year old and a 21 year old can have sex.

Is a 22 year old dating a 18 year old weird?

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.

Is it okay for a 24 year old to date a 18 year old?

It is not illegal for a 24 year old to date an 18 year old.