Can i use an old apple keyboard with a new MacBook Pro

I have just bought a new MacBook pro, which has wiped my bank account, obviously, and I connect it to a separate screen just a dell one so I have double screens but all; my stuff stays on the MacBook.

Anyway, my current keyboard, again an old dell one, has finally died and i want to get an apple keyboard, but not a brand new one as often i work directly on the pro itself only for editing work i plug it into the screen and open up both screens.

If i got an old apple keyboard, would it connect properly to my new MacBook? Some people have told me no not if it's a brand new MacBook and 2009 or 2011 keyboard, but some people say yes it's Bluetooth so it will work.

Before investing EVEN MORE into my work equipment, i'd love to be sure!

Thank you!