I don't think Philly's is as old, but yeah it is pretty old. San Fran's is relatively new, but yes, I think DC;s is actually based/designed from BART.

Take a look at the cars from DC and compare to BART's, very similar. Baltimore has a small subway, as does Cleveland (or at least they used to).

LA's subway is the newest in the US. Boston, New York, and Chicago's are the oldest.

For North America, Toronto, Montreal, and Vancouver have subways. Vancouver's was built in 1980's, and is completing a major expansion next year. I think Mexico City has a subway.

Those are the only subway's Im aware of, besides Atlanta (I think theirs MARTA is subway, but it might be LRT).

In Japan, most major cities have subways in addition to overhead trains and commuter rail (and highspeed rail - shinkansen). Tokyo, Osaka, Nagoya, Yokohama, Kobe, Kyoto, and Fukuoka have extensive subways. I think Sapporo might but I dont know for sure.