According to This Lesson the term "güzelim" is only used for girls.

Why???

How would you show the same sort of compliment to a boy?

you may say yakışıklı = handsome ,
hoş = nice, cute
karizmatik=carismatic
charming=etkileyici, çekici...

Hmmmm hoping I understand where you're coming from, bod...
If you really want to call a guy 'beautiful' you can get away with güzelim. Though, if he's turk (and straight) I really wouldn't advise it.
On the other hand, I get away with calling some of them 'beautiful' (using english) all the time.
There's that very subtle distinction which many people may not notice or acknowlege (or appreciate).

ok? was I on the right track?

Because the word itself indicates the feminine. And where we may not equate 'beautiful' with femininity per se, in this case I think it would be taken that way.

This is only my guess, bod. Certainly you gave a more specific idea in your last post of what it is you're after. Maybe it will make more sense now to a native turkish speaker.

Bod! I think you have an excellent point in this discussion! It is strange indeed that beauty is considered to be a strictly feminine attribute (no, not strictly feminine, also cars-related, objects-related, animals-related - no matter what the gender , etc...). Nowadays, it's probably more of an instinct then a thought of thing but the culture surely plays a role here.

To tell about physical beauty of a man, we use "yakışıklı" which means handsome. So, I think there's no problem.

but for your dog, you can say "sen güzel bir köpeksin" regardless of his gender, but if you personify your dog, then it means you consider its gender and say "sen çok yakışıklı bir erkeksin" or if it's a female you say "sen çok güzel bir kızsın"

but now I'm thinking and for little sons and for children you can say "güzel". "güzel oğlum benim" "my beautiful son"

so you can still say to your dog "güzel oğlum"

but nooo, you won't be a father of a dog if you say "oğlum" to him.
I don'T know how people call their dogs over there, but here people call them "oğlum" or "kızım" which shows their love for them.

Believe me bod, Turkish ladies can be very creative when it comes to terms of endearment.

"Güzelim" between mature men is almost a generally recognized code between gays.

I wouldn't want to call a man 'beautiful' in English, so why would I want to do it in Turkish? Women are Beautiful and men are handsome easy!

Although men can be beautiful inside

another one is "tatlım"... only for a girl...

Bod, I definitely think you should not say 'you are beautiful' to a turkish boy, especially if you are in full make up, your skirt and those cute pink furry boots!