AbdulAlhazred
Legend
All you needed was a 19 Int to cast 9th level spells if I remember correctly.
Now Hussar I'm still not sure where you are getting your info from but game goes from level 1 to 20 so the game is in fact geared for it. You can't ignore levels in order for your argument to be valid. The games default is 1 through 20 so my argument remains perfectly valid and correct. Having access to 4 more levels of spells trumps the elf all day long.
18 INT. 1e actually doesn't contemplate PCs ever going outside the 3-18 range except for a few +1s due to racial bonus that allow for instance an elf with a 19 DEX. In fact you can raise a stat by one using magic, but it is VERY hard and unlikely to come up even once in most campaigns, even then the racial limits apply AFAICT.
As for D&D being 'designed for 1 to 20' this is nonsense. 20th level is not in any way notable in D&D before 3e. Some charts in AD&D go up to level 29 and BECMI has levels that go much higher, though I agree with Hussar that they're more of a separate game. The point is you can't really point at a specific rule that marks a cutoff in levels, by AD&D rules a character can continue to advance forever, though there are few specific advantages to levels beyond 17th. This is interesting because what it means in a practical sense is you can't say that the rules are very much evidence of anything one way or the other as to what level the game was designed for. Clearly for wizards there are substantial rules for up to level 17 (9th level spell acquisition). OTOH even wizards get very little else after level 12 and the 7th level spells they have at 13th are very nearly as potent as 9th level spells (and were in fact at one time in OD&D considered "magic beyond what PCs can do"). Personally I've always considered levels beyond 9th 'capstone' levels, and beyond 13th pretty much just filler material that is rarely used in play for PCs but is more useful as a way to gauge the power of super high level enemies.