If I fell like that now, would I still bounce back up unhurt?

Generally no, simply because you are now heavier and taller and longer-limbed and as a result all the injury-causing forces are much larger.

I’ve seen kids try and do a backflip and land on their neck and get up laughing. If I tried that? I’d be fuckin’ DEAD.

If you rag doll again you may be fine, people hurt themselves when they lockup falling. Try penguining next time.