24 is the level for ancients.
25 and above will level very quickly in normal baal runs until ~45. Normally people stop at 40 and get rushed in NM. 41 and above will level very quickly in NM baal runs until ~75. Then you know what happens.
i level up fine by just playing through, but i always finish a4 by 23 or 24, and i know i don't get jack in a5. i can do the ancients, but it doesn't help at 23, i'm still stuck afterwards. if i hit 25 before i do a5, i can hit 29 by playing through, just right for all my midlevel eq.