I bought my first packs of both baseball and football cards in 1970, when I was seven years old. Kept buying packs until 1975, except for 1971...still can't remember why I didn't collect in 1971 though.
In 1975, I bought my first cards through the mail: the 1975 Topps team sets of the Reds and Padres, through a Larry Fritsch ad in The Sporting News. Started buying baseball complete sets in 1976 from Fritsch.
Bought my first pre-WWII cards in 1979: T206s of M. Brown, Keeler and Bresnahan for $10 total.
I haven't stopped since
Steve