Electrical - you don't know the condition of the wiring until you really look at it and I presume you had not, you just looking at switches and powerpoint that seem old due to age. If the internal wire are of good quality then no need to redo wiring, just change the switch and powerpoint to new one.. then its completely new. Older wiring of good quality can last for years and can even be better than current wires... EG now the wires only come with single layer insulation, those older wire may come with dual layer installation and outlast any single insulation wire available currently.
Plumbing - this may be an issue.. as think if 20 years old that time it could be metal pipe that could form rust issue, not like current where all "plastic". This is also dependant on how the owner maintain it. If manage to kept internal rust at bay, the pipe work could be even more "solid" than current "plastic" pipe. Just you need to change all the tap and such to make it more modern looking if you fancy it. If the owner have external filter that kept the metal pipe clean then it can be said its better than the current.

Don't look down on an old Condo.. it may look age out but as they say Old is Gold... workmanship and material quality from those days could be as good or even better than current age where so-called cost saving had crept in.

If still unsure, can hire a professional to go in and do a proper evaluation with the current owner consent...

Lastly, don't simply listen to friend blindly, even when they have good intention.