Is it different to compliment a boy?

I have been reading around on how to say 'i think you are beautiful'/'you are beautiful' but I know some languages have different ways to compliment between boys and girls (if that makes sense), I know a little Japanese, but I'm pretty new to the language so I don't know if saying something like kawaiine or anatawa totemo kireidato omoimasu would be insulting or incorrect to say to a boy? Sorry if this has been asked before!

It depends on the individual, most of my Japanese girl friends only say a boy is kawaii when he is a small child, or perhaps a particularly endearing little ojiisan.

Usually when talking about guys we find physically attractive, kakkoii or ikemen do the job.

In English you'd probably use "handsome" or "good/cool-looking" for guys while you might use "beautiful" or "cute" to girls (traditionally speaking), I assume?

There are similar differences in Japanese too. And I agree with LIZ above that "kakkoii" (cool-looking) would suit better. "Ikemen" is also "cool/good looking," but if you are thinking of saying it in your formal speech sentence, it might not really fit in :) (But this is coming from a Japanese woman in her early 50s, so maybe young people say it all the time :))

thank you for the replies! would saying 'anatawa kokkoii' be saying 'you are good looking/cool?' Sorry for posting another question, I have trouble putting together sentences sometimes!

I don't know how close you are to that person, but a bit more informal like:
- xxx-san, kakkoii desu ne
- xxx-san, kakkoii ne
(Both say "xxx, you look cool")
or
- xxx-san wa kakkoii desu ne
(You look cool, but using the name instead of "anata")
... might sound less stiff :)