Is a 25 year old dating a 19 year old weird?

Is it weird for a 25 year old to date a 19 year old? Yeah, its fine. If you love each other, and are both above 18, you guys can be together. I dont really think anything is wrong with age gap relationships, as long is its nothing creepy like a 14 year old and a 30 year old.

Is a 19 year old dating a 13 year old legal?

It is not illegal for a 18-year-old to have a social relationship with a 13-year-old of the opposite sex, it is statutory rape however if there is any sexual activity between the two parties.