Holmes version (my initial encounter with D&D) was over my head, I was 10 at the time. My dad had to help me with rules and I just sort of winged it with my friends. For a bit I DMed just using the rule reference/summary page from B2 when I misplaced my Holmes book
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When I got to AD&D (age 14), I had the advantage I'd already learned D&D through the Moldvay books (age 12).
I don't remember AD&D being too difficult to understand, but I do remember it being complex enough that I was hand-writing the rules for the PHB, DMG & UA all in one book for easier reference and having them in one place. Coming from B/X, there were quite a few AD&D rules that I just didn't use (Weapon vs. Armor, Psionics and Bards, for example).