As I said in your discussion post, men often don't like it when women call them beautiful. However, it's definitely not wrong. In fact, if you do a search for the phrase "beautiful man" in Google, you get 11,600,000 results. So clearly a LOT of people think it makes sense to call men beautiful. I think this is especially true when women talk about celebrities (actors, musicians, etc.) that they find attractive. The phrase "a beautiful person," which you mentioned in your other post, can certainly be applied to men. If you say "a handsome person," you're just talking about physical appearance. If you say "a beautiful person," you're mostly talking about someone's personality and character.

A very interesting question because it's not technically wrong to call a man "beautiful" but in most, if not all countries, it is considered very strange because they have separate words in their language for describing mens and womens good looks. The norm in society, globally, is to call woman beautiful and men handsome. This is more about the semiotics of the words and how they have always been used historically but they do basically have the same meaning.

I think you can call it, there is nothing wrong with it. But if he does not like it, his choice,you shouldn’t :)