What should you do when you like a guy that's 18 years old and your 14 years old?

See love not always means sex. Love means to people happy with each other and can trust each other.And again you both are at a very raw age for all these things.So being in company with each other is not at all a problem whatever age you both are.
When you will be friends and if you like each other and decide or believe that you can stay in a relation with each other age again will not be a problem in future.May be at that stage it will not be even a question for you.
Medically also this little gap is age is not at all a problem anyway.
So,what I suggest for now is be friends . At least be with each other and wait for the coming times to decide .
And anyway for a girl hiding her age has never been a problem.Well after sometime when you people will be comfortable with each other you can discuss this with him and I guarantee you , no harm it will cause to your relation then.

Enjoy!!!