I was around 10 yo and it was a Sinclair ZX-80 (circa 1981). Later I had a Commodore VIC 20 as Xmas gift. I still remember spending two days of barely eating something and trying to figure out how it worked. too excited!
It had a dead tape-deck though, so I mostly read the manual(s) and typed "10 PRINT "HELLO"; 20 GOTO 10", etc.