I disagree with 2 of the above posters who imply that it is not very useful, to put it mildly.
I 'got it' when I was about your age (one year after having started playing). Not as easy to get on tenor than on alto, but I used it on tenor a lot (mostly for fun) during band practice.
Try on the upper octave first. The size of your cheeks have little to do with it on the sax, it's not a trumpet. It's not necessary to use your cheeks much. The way I do it most of my air reserve is under the upper lip, not on the sides of the mouth.
Practicing with a glass is not very helpful IMHO, you have to "get it" in a mouthpiece situation. Maybe practice with mpc+neck.
As you become more at ease you'll be able to expand the range of notes from upper octave downwards.
The other day my wife went to a concert and the clarinettist (Alexander Fiterstein) was using it all the time (had very very fast passages to perform).
My view on circular breathing is that if you know the technique and master it on a good range of notes it'll be one more tool in your toolkit... that may come handy at some point (very very long notes to hold, trill, etc). And in these situations you'll have an edge over those who don't master it or those who consider it as an oddity and/or haven't really tried hard at it (as various comments in other threads on the subject suggest -- do a search, man!).
Good luck! I commend you for trying and getting interested in this technique!