actually they look same age....I can kinda tell.....also look carefully, you will see that the double guys that Ian posted has the same mount bracket as above......so the arm and the fixture is pretty much the same age
we have these type arms all over my city..and they also appear to bend at a downward angle...not sure if they were intentionally like that or the weight of the heavy Mid-Sized Cobraheads on the old steel.