While the first three games certainly set most of the precedent of standard Zelda gameplay, Ocarina of Time was a trendsetter for all modern games of its genre. Z-targeting alone (or whatever button we hold for lock-on nowadays, it seems to change all the time) was used by several other N64 and...
I never thought a game's "classic" status was necessarily dependent on how many years it's been out. Katamari Damacy is definitely a classic to me, though it's much newer than Ocarina of Time. I'd even consider Portal to have plenty of classic-worthy attributes. And come on, isn't ten years...