Absolutely!
Jacko was 5 when she came into my life---she didn't play, was terrified of hands/toys/new things and didn't step up or really do anything but pluck.
At 13 she plays fetch (which she loves lol), rides in the car, wears a harness, meets new people all the time and beak grinds the whole time, she is afraid of almost nothing new (total time adapting to an entirely new house---maaaybe 5 mins), eats *anything* and wants to chew on or get into EVERYTHING

.
She also flies now (a bit like a graceful brick---or a helicopter

) and is a pretty self-confident self-directed bird (she goes where she wants to independent of me and I think the ability to be self-sufficient and in control of her own life has helped immensely).
Are we a hundred percent there yet? Nope. I'm still working on the physical repair of her body (chronic malnutrition and its impact on the body or feather/nail neglect can take a looong time to correct), but she's come a long way and I see her continue to improve inside and out daily. One day we'll work on the flight commands, but until then I enjoy watching her look and feel better with each passing day.
She still isn't cool with being toweled for example, but loves to be huggled and snuggled under a blanket with me (we tend to have lazy in bed days when we feel like it) and will take a nap cuddled up to me like that---so again, we is getting there.
Just let Sam guide you---and the biggest thing for me would be to get him onto a better diet ASAP. You can work on the toys and etc as you guys go along. Believe it or not I'd schedule a vet visit for some bloodwork ASAP as well---you can thus be the 'hero' who rescues him from the big scary vet after they're done---which will help him like you. It'll also give you a guideline to how his organs etc are holding up.
Good luck
