How Do I Get My Old Singing Voice Back?

It's going to change until you are like 15. By the looks of it you are probably going to become a base, instead of a tenor [higher male registrar of voices]. Some people have gradually changing voices, but some change all together like yours. Luckily, mine changed very gradually and I was able to keep my tenor singing voice.

yep.

you will not be the same after puberty but you can still have a good voice if you practice :D

go a lower octive of course! It's now very shaky because you're singing too high.

It will never be quite the same...

To some extent, practice -- if you keep warming up, every day or at least a few times a week, as high as you can go, your range will extend in that direction. But some of this is just physical -- there's only so far you can stretch your range before it's just not physically possible anymore, so you might just have to adapt to having a somewhat lower voice.