There are so many variables that I don't know that there is anything such as an "expected life" of electrical equipment. There are many electrical systems in place that are more than 50-years old that are still performing adequately and there are probably some that were installed last week that should be replaced. Some of the variables are:
The environment in which the equipment is installed (damp basement, or nice, dry, climate controlled room?)
The quality of the original equipment (was it a good recognized brand for which replacement parts are still available, or the cheapest junk that was available at the time?)
How heavily is the equipment loaded.
The workmanship of the installer (were connections properly torqued, etc.)
Has the installation been properly maintained?
Has the use of electricity increased and is the equipment still adequate for today's electrical load?
I don't think anyone could make a blanket statement that any electrical system over ?? years old should be replaced. Each installation will need to be evaluated on its own merits.