No offence but I'm turning 13 in 2 weeks and I've only looked at a couple green anacondas and I could say a little more "experianced" stuff then you could...

Most green anacondas are aggressive, yeah, you can tame them down a bit, but that doesn't gaurantee that its going to be a nice cute snake for you.
The majority of green anacondas do bite and are quite aggressive.

My best guess would be to own A jungle carpet python for a start and then work on a blood python even then that's not even close compared to what a green anaconda is going to be like.
Even if you were to get a anaconda, as said start with a male, they're generally smaller then females and that would be a start.