What is the OLDEST military aircraft type still in service

I have wondered for quite a while now, and hoped some of you may answer it,

I Love 1950s aircraft , especailly military, And i wondered , What is the OLDEST serving Aircraft type in the worlds airforces to date, ??
I would really love to know, I even wonder if some airforces still have Mig 17’s
or something from that vintage,

Any clues would be Most helpful
thanks in anticipation
Chris C