IF you want to be a GREAT opera singer, then you will simply start today doing EVERYTHING you can to achieve your dream.
IF you are looking for some sort of equation (X-years+Y-Courses=Opera Singer) then have fun frustrating yourself.
Above all, Opera singing is an ART, and ART defies concrete analysis.
There are WONDERFUL Opera singers who never set foot on a university campus.
You need at least six things to "learn" to sing opera:
1. A personal voice coach.
I seem to recall you posting before and saying something about taking lessons.
Obviously you didn't like the advice or answers given by your teacher, or you wouldn't be wasting your time asking for the opinions of strangers here.
IF you do not have a personal voice coach who you are willing to OBEY, then your dream is over before it ever started.
It sounds to me as if you are asking people to justify your distaste for YEARS of schooling.
Look at it this way: IF you don't have the talent, schools of higher education won't accept you for their advanced degree programs.
Instead of wondering how you can get around the need for higher education, you should be focusing on learning how to do MORE than your competition.
2. A foreign language coach. This may be your voice coach, or someone else recommended by her/him. In any case, they should be "on the same page" so that they don't contradict each other in your lessons.
3. Hours and hours and hours of listening to great opera recordings.
4. Regular attendance at "World Class" opera performances.
5. Piano lessons. This is the best way for you to learn your music theory and become your own accompanist.
6. DISCIPLINE: YOU are going to have to suck it up and simply do as much as you can every day to improve yourself.
IF you do all these things, and IF you have a natural gift and/or talent, then MAYBE you won't need a degree.
You can perform everywhere possible.
Those who direct your performances will let you know if they think you have more promise.