Advice on basic singing/pitch problems and Opera singing for beginners?

I'm 15-years-old - nearly sixteen - and I'm very interested in Opera.
Opera, broadway and musicals - I love it all, but Opera is my main
concern at this moment.

How many years does it take to develop a perfect - well, it can't
literally be perfect, but that's beside the point - Opera singing
voice worthy of using on a stage? I realize it may be different for
many other people, but is there any way I could have an idea of how
long?
And though I'm working on this dream, my voice is horrible, I think.
It cracks a lot, I can't go too high without sounding out and I'm
totally off pitch at many points! Also, my voice sounds alright to me,
but when I record it it sounds worse than I though. How can I fix my
horrible pitch problem and how do I make myself hear my ACTUAL singing
voice and not what I hear in my head?

I'm trying my best, but I feel like it's useless and I'll never get
anything done. Can someone -never- be able to sing beautifully even if
they practice a lot? I fear my voice will never get better, though
I've been doing online lesson things - since I can't afford REAL ones
- for 2-4 months now. Shouldn't it of gotten A LITTLE bit better by
now?

What are some basic exercises for Opera singing and songs for
beginners to practice with? Any other advice I should know, since I
know so little, would be greatly appreciated!

And I'm sorry that this question is jumbled up like and silly. I just
don't know what to do.
Thank you to anyone who is willing to help!