There's stuff rolling around Romania that is very 2nd or 3rd hand, including some of the ex-Danish Railways Ansaldo-Breda built IC2 DMUs that even the Danes couldn't get to work. I'm not sure the Romanians are having much more luck! There's also a large number of ex-SNCF DMUs which have been titivated locally by Romanian coach and loco builders. They're having a lot more luck with those on little branch lines in the outer reaches of Romania.
The Swiss have only recently retired some narrow-gauge stock which was pushing 60 or 70 years old. But they were well built, well maintained electric units, which will go on more or less indefinitely if you look after them. I think some of them have been sold to Eastern Europe as well!
The place to look is on the EuroCity routes, plenty of 1960s West German Compartment Stock rolling around on that.
IIRC OBB are replacing the DB/CNL Night Train stock they bought to restart night trains and that's of similar age too.
What was obvious was that it had all been rewired and significant maintenance work done by Siemens in the 90's... because under the builders plate was a Siemens plate telling you about the refurbishment!
THe oldest of the swedish stock appears to be from the late 1950s, depending on what you get it's either been refubished in the last few months, or a few decades ago!
Given that bogies can be swapped out, metal welded and everything else can be renewed (and should be renewed at sensible intervals) there's no excuse for coaches not to be of that sort of age, and with the likes of the HST engine replacements should give them another 20 to 30 years from that point in time provided the chassis and skin are maintained.
Multiple units may be a bit different due to the effort needed to re-engine them?
Talking of the Danish IC2 for hopeless modern Stock, I raise you Fyra...
Actually there's a common theme there... AnsloBreda...