The data plate was missing on this unit so I was looking for a little help.
“The age and BTUs can’t be determined because the date plate was missing.”
You can use it. 
Exactly…“and do recommend preparing funds for replacement as need be.”
I would use the above recommendations. One other place to check is in the utility room, possibly by the electric panel, some installers leave the owners manual and whatnot hanging with the rest of the paperwork for the utility room. You can find good stuff here if you take the time to look through it.
It may be stolen. :shock:
If you have a stolen A/C unit will it only blow hot air? :-k