First gig ever was a party for our high school class when I was 14 (1977).
First paid gig was at the opening of a bar/bistro/dancing that belonged to a friend of a friend.
First pro/resident gig is a longer story. Saw an add in a national newspaper in Holland, asking for DJs (german and english speaking) for work in Europe. A phone number to call before saturday evening 20:00. I called sunday evening at 20:45. Got invited for an audition in Club Juliana’s in Amsterdam the next day at 16:00. Got a call at 20:00 I was hired and to get ready to leave in a month to a place yet to be determined. Got a call that thursday afternoon if I could make it to Essen, Germany by friday afternoon :-D. Packed my stuff, told my daytime job boss to shove it and had my dad drive me to Germany. Got 1 day of hand-over and was solo on saturday night.
The rest, as they say, is history.