Is it weird for a guy to like a girl older than him? Is it weird if a guy and a girl older than him are dating?
In general, no, but there can be concerns depending on the ages involved. There is nothing odd about a 25 year old man dating a 28 year old woman. However, when a 15 year old guy is dating an 18 year old gal, it might be an indication of a problem.
Girls reach maturity earlier than boys, so girls typically find boys their own age too childish. Most teenage girls find themselves attracted to older men. So when an older girl wants to date a much younger boy, it indicates that she wants a guy she can control.
A teenage boy who is much younger than the girl he is dating finds the situation to be an ego boast. But that pride then makes him vulnerable to sexual sin as he tries to prove he is a man, but doesn't have the experience and the foresight to see the dangers in having sex before marriage. Often his emotions take over and he doesn't think the situation through as he should.
So what about, for example, a 14 year old guy liking a 15 year old girl. Would that be weird, or a problem as you were saying? If not then what about a 13 year old guy liking a 16 year old girl? And I am not just saying is it weird (or could it be a problem) if they were dating, but I think I also mean if the (younger) guy liked the (older) girl or the other way around.
A year or two difference in age is not a major issue at most stages of development. But let's take the 13 year old guy. At that age, he would typically be in his growth spurt -- about halfway through his changes. A 16 year old girl is typically just about done with her physical development. A relationship between the two at this age could lead to problems. I would typically advise just being friends and waiting a few years until the boy is closer to maturity.
Generally, it isn't advisable to seriously date someone until your are pretty much through most of your development. In the middle of it, your hormones fluctuate wildly and might cause you to do rash things you would later regret.
But if you are talking about friendship, a person can like someone of any age or any gender.