Started in 1978, 2nd grade. I said a year or so, but don't recall specifics. We (friends, classmates, brother) bought anything we could afford as soon as we could save up. Some of our early non-D&D purchases were Runequest, Gamma World, & Star Frontiers. I think the second round included; Tunnels & Trolls, Gang Busters, Top Secret, Twighlight 2000, and ElfQuest all before AD&D came out?
Hard to answer, as I started playing D&D in the 1970s. There weren't other options right away. The "other" games were Monopoly, Risk, Sorry, etc.
Actually, for the time there were a lot of games released in the 70's. But, distribution was another matter. Luckily we had a Hobby Bench that tended to carry RPGs.
Wikipedia says: Empire of the Petal Throne (1974/75), Metamorphosis Alpha (1976), Traveller (1977), Chivalry & Sorcery (1977), Arduin (1977), Superhero: 2044 (1977), RuneQuest (1978), and Gamma World (1978).
Then I played Gamma World - which was really just reskinned D&D.
NO!!! You could roll up a two-headed mutant with psychic powers. It was not the same! Well, to a ten year old they were very different. But by today's enlightened standard? Yea, just flavor and some new tables.