I'm 16 and have been playing guitar for 8 years.
I've always dreamed of being able to sweep like synyster gates, but I am still terrible at it.

Is it just me ? Am I doing it wrong? What could it be?
It is a technique that requires some finesse, there's only so much that can be taught, there is an element of exploration involved.
I'm just a kickin' and a gougin' in the mud and the blood and the beer.
Muting. Start focusing on your muting. It's the most important part of sweep picking.

I also might add that Synyster Gates has been my idol since i was 15 too. I'm 21 now
Not sure man, I do know what you mean though. I personally am more satisfied and impressed with myself with comprehension of music theory, picking things out by ear, but not so much the "fancy" fast stuff.
Guitars: ESP LTD H-1001FM ACSB, Epiphone SG Special
Acoustics: Fender Hellcat, Mitchell 12-string
Amps: Roland Microcube, Peavey Vypyr 15W
Effects: Digitech RP355
Thanks guys for your feedback and support.
I'll keep practicing and maybe look into a metronome.
Do you practice sweeps? Even if you've played for 8 years if you've never practiced sweeps then you're not going to be able to sweep.
It's worth mentioning that it doesn't matter how many hours a day/years you've put it, it matters what quality those were.

If you practiced poorly (bad technique, bad posture etc) that won't help at all, no matter how much you practice. Practice does not make perfect, practice makes permanent.

Making sure you are doing it perfectly at slower tempo and let it develop naturally is probably the best approach.
Fusion and jazz musician, a fan of most music.

Quote by Guthrie Govan
“If you steal from one person it's theft, and if you steal from lots of people it's research”

Quote by Chick Corea
"Only play what you hear. If you don't hear anything, don't play anything."