Eye Candy means a man or a woman that is good-looking. We wouldn't say you are AN eye candy. It is an uncountable noun so just "you are eye candy to the young men here" would be fine, for example. You might ask your friend "why do you always go to that Starbucks coffee shop?" and your friend might say: " The coffee isn't that good but i go because there is a lot of eye-candy there!" Haha.

In the US we would say "I think you are just eye candy", without using an article before "eye candy". Saying that a person is "eye candy" means that they are physically and sexually very attractive, either a very beautiful, well-proportioned young woman or a very handsome, athletic-appearing young man. Depending on context this could be a compliment or an insult. Saying that a person is "just eye candy" means that their physical appearance is all that matters, and that their intelligence or education is not important. "Just eye candy" is never a compliment, and it almost always is an insult.

It means you are aesthetically pleasing, you look good. This can be used as a compliment between familiar people. However, if the speaker has placed the word 'just' before the compliment then this can imply that you are only good looking and have no substance (you're shallow), and this is not a compliment.