isn’t four and a half years ago a bit long
The cut-off is six years, after which time it becomes “statute barred” and unenforcable. This time scale resets if you admit to the debt. So yes, they can ask for it.
After that length of time though it seems curious that they’d go straight to threats without simply asking for it first. Have you had previous correspondence?
Ordinarily I’d say that it’s a third party company who are chancing their arm and suggest telling them to do one (there was a thread here a week or so back, search back). However, if they’ve provided proof of the debt and you’re pretty sure it’s correct, I don’t think there’s a lot you can do other than suck it up.