How old is old? I use Debian on an 11-year old cheap laptop, and it runs fine. No GNOME, of course (it's the performance equivalent of Windows on pretty much any hardware).
The laptop was something like $300 back in 2012.
without GNOME and disk encryption, of course you can run Debian on a toaster
Encrypted disks would be the key issue here, older CPUs likely can't handle the encryption work required.