Slow Spell: A broad-area spell which effects up to 24 creatures in a maximum area of 6" x 12". Duration: 3 turns. Range: 24".Since the quantifiable effects of these two are basically the same, they can be dealt with quickly. The range of 240 feet fits what I've been referring to as "Line of Sight" range for combat spells. Likewise, the 3 turns duration is close to the 2 turns suggested for brief in-combat effects. Perhaps "Brief" should be changed to 1 turn per spell level, minimum of 2 turns?
Haste Spell: This is exactly the opposite of a Slow Spell in effect, but otherwise like it. Note that it will counter its opposite and vice-versa.
The weird part is how to deal with the area of effect; it's a rectangle twice as long as it is wide. Can the rectangle orientation be chosen by the caster? Would it be too horrific to pare the area of effect way down to the flat 30-foot diameter circle suggested for Light and Fire Ball? Or should some separate category be created, and if so, what would the criteria be?
I'm actually leaning towards the reduced area, myself. Sure, that reduces the potential effect, but in exchange, we could drop the "24 creatures" restriction, since you are unlikely to fit more than 24 man-sized creatures in a 30-foot diameter circle.
Note that neither the Haste spell nor the Potion of Speed (in Monsters & Treasure) mention aging effects. It's true that OD&D had no aging rules, but on the other hand M&T does list a Longevity potion and the aging effect of a Staff of Withering.