I read my first Trek novel about 37 years ago, I'd say. And my 40th anniversary as a Trek fan will be this coming January.
For a long time, "Trekkie" was seen as a derogatory label applied to Trek fans by those who looked down on them -- akin to "hippie" or "groupie," or maybe even "junkie." "Trekker" was coined as a more respectable alternative, by analogy with "trucker," I think. (Or perhaps simply from the Dutch word trekker
, one who goes on a long journey.) These days the stigma attached to "Trekkie" seems to have been forgotten and the terms are used pretty much interchangeably.