I've always heard 25-30 years stated as the recommended rewiring
schedule.

Even Electrical Safety First doesn't push such nonsense. They state
explicitly[1] "There are no set guidelines as to when a property should
be rewired. Just because your wiring's old, it doesn't mean it's unsafe.
Many factors can affect the wear and tear of your electrical
installation, including the materials used and how your property has
been used." And that's from a charity who generally lose no opportunity
to get people to spend more money on electricians[2].

[1]
http://www.electricalsafetyfirst.org...ked-questions/
[2] which is not to say that's anything other than a very laudable
purpose in life

--
Robin
reply to address is (meant to be) valid