It’s a normal expression. It work in French (even in French Canadian)

Edit: As we talk gosse, I wanted to add a Canadian point of view on the word.

The word could mean more than one thing here, it depend on the context it’s used in. I will add some dérivative of the word.

"beau gosse" mean the same thing for us than in the Francophonie. (synonyme; beau mec)

"Tu me gosses" (Synonyme; Éxaspèrer)

"J’ai mal aux gosses" (Synonyme, Testicules)

"Il n’arrête pas de me gosser avec ses commentaires." (Synonyme; Éxaspèrer)

"Arrête donc de gosser, on va être en retard à notre rendez-vous." (Synonyme, Perdre son temps)

"Quoi ? Il faut remplir tous ces nouveaux formulaires ? C’est rien que du gossage inutile !" (Synonyme, Perdre son temps)

"C’est gossant à la longue. Chaque fois que je me présente pour mon rendez-vous chez le médecin, il arrive avec deux heures de retard." (Synonyme; ennuyeux)

This is an expression subject to social context in a high degree. Do you mean you want to translate "handsome kid", or is it that you want to render "handsome man" or "good looking boy"?
This is an expression that has belonged to the youth culture, the teenagers. It has slowly seeped upwards, although recently certain writers have taken to it like duck to water, but it is still not at all the proper expression to use for adults, in particular men endowed with a certain virility: they are not kids and « gosse » is nothing else but "child", in a popular/colloquial register. The American cultural trait consisting in calling men colloquially "boys" does not exist in the French culture¹. For example, I don’t think that fourty years ago Alain Delon would have been pleased at being called "beau gosse". A cue tending to show that there does not exist yet a universal usage of "beau gosse" in the way of speaking of the beauty of men is the literature, a rather light kind of literature, but I believe it is representative of the society, that is, at least in part; this literature, for the mass of it, dates from after 2010, which is the indication that the writers didn’t before that time identify the expression as quite proper (ref.).
However, today, young movie stars and the like will find that locution less inappropriate and even use it themselves occasionally.
Nevertheless, one must not forget that the traditional expression use to describe men endowed with beauty, that is "bel homme", is presently used in the written material five times as much as "beau gosse", fact that can be gathered from the following ngrams (ngram 1, ngram 2), a copy of which is found below.

This shows that "beau gosse" does not satisfy a lot of people and you have to be careful if you really want to use this locution. Another cue showing that this is not a term that is proper in all cases is its register, which is popular.

(TLFi)− Pop. Beau, belle gosse. Beau garçon, belle fille.

The ngram below shows that the expression of standard register, "beau garçon", which can be used without risk of an error for men in their late teens and young men is itself used today in the written material approximately three times as much as "beau gosse".

You can use this locution if you are young enough and if you are among young people, and, moreover, if you apply it to rather young people. It will be found bizarre if you use it in speaking about Donald Trump whomever you are speaking to in France.

¹ _{Except in an indirect way in the restricted context of an occasional idiomatic expression such as for instance "vieux garçon"; this one means simply "homme célibataire d’un certain âge" (middle aged bachelor).}

Assuming the meaning is "I think you look handsome" while speaking to a boy or a man, yes, that’s exactly how "je te trouve beau gosse" is used. It can also be abbreviated to BG, as already mentioned here.

There is just a small warning, while the expression still seems acceptable in a French Canadian context (see yagmoth555 reply), beware gosse happen to have also a very different meaning there.

Otherwise, despite what you might have read elsewhere, there is absolutely no usage restriction regarding the age of either the person speaking or the person they are talking about, beau gosse is just mildly colloquial.