My classmate used to watch seasonal anime and has watched around 300+ shows before we graduated high school a year ago.
I think you're pretty addicted to anime when you do that. Also, when you fork over bales of money for figs, LNs, tank compilations, have a waifu, funpost on /a/, and that kind of stuff. Well, those things aren't bad in themselves unless it adversely affects your social functioning, or unless you shape your whole personality around a "OMG anime is muh life !!!I wish I get born again but Japanese!!111!! Nihon bestu cOuntry desUUuu~" mindset.
Personally, I think anime is one of those things where being a casual is better than being a hardcore fan. I like anime a lot and have watched quite a few shows, but I can't say I'm addicted to it. The last series I watched was Amagi Brilliant Park, and I watched it over a year ago.