Examine the rear hub for a date.
Before you ride it you need to decide if you will keep the wheels, probably not. If the hub on the front wheel has an oil port it might be worth preserving. The rear 3 speed might also be worth keeping, although if you plan to ride it you can replace the hub with a much improved modern version(see postings for internally geared IG hub).
Otherwise it looks like the frame is solid, and desirable. I would keep the old style handlebars, but that is very dependent on what you plan for the bike. I would also use a saddle with springs if you keep the old handle bars, as you will have an upright ridding position.
I also like the bash guard with the circle cut outs, It would be nice if that could be preserved somehow.