Theres not really anything illegal about the 18 year old dating a 15 year old. However, it gets to be a legal problem if dating means having sexual relations. If you are having sex with this 18 year old guy, then he is committing a felony offense that could make him a sex offender.

Can a 18-year-old legally date a 30 year old?

Yes, its legal.

Is it bad for a 14 year old to date a 18?

If you are 18 and she is 14, you could be arrested and charged with serious sex crimes, even if you dont actually have sex. Even kissing a 14-year-old can be charged as a felony in California. Thats the kind of crime that can stick with you for life.