I believe 60 amp services started coming in during the 1920's when they started grounding the neutral and prohibiting fusing the grounded leg.
I have seen a 100 amp round meter socket, deeper and larger lugs than the 60 with two 60 amp panels connected to it. This was installed right after WW II when alterantive materials were not available.
The 1959 NEC was the first edition to require 100 amps based on calculated load, and / or number of circuits.
There are still twelve 120 volt 30 amp services in operation in my city.
(and I know where they are