When did the 60s youth counterculture start?

Now I know "60s counterculture" is a vague definition and the civil rights stuff and underground stuff was going on since ever since the decade started, but what I mean is the youth counterculture and the surging popularity among the youth and the rock stars Jimi Hendrix and John Lennon and Bob Marley.
1967
1966
1965
1964
1963, right after Kennedy died.
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When did the 60s youth counterculture start?
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