Per the UPB description - "The Power can accelerate or reverse the aging process. The normal rate is multiplied by the Power rank number, For example a Good rank can make the aging occur at tenfold rate or go in reverse at an equal rate..."

Normally I can figure stuff out on my own, but this one is stumping me. "Normal rate" would be that a target ages 6 seconds every round (6 seconds), hit the target with Good 10 BC - Aging and they age 1 minute in 6 seconds.

I'm getting old, but I really don't feel any older than I felt a minute ago, even 10 minutes ago LOL. BC- Aging at low ranks, it's negligible. Even high ranks aren't all that: Even Class 5000 BC - Aging would only make someone around 8 hours and 20 minutes older or younger per round.18 seconds later (3 rounds) you've aged or de-aged the target by a day. You could die of boredom trying to age a target to death. It by its wording doesn't seem to have the real "instant old man" effect that was probably intended.

You could boost that per round effect by 5000 times with Class 5000 Reality Alteration - Temporal Flow, but that only gets you to aging a target by around 4 years and nine months per round,

Am I reading the UPB wording wrong? It could be, I am getting old...

I think it's a simple multiplication of time. Like the aging at a Good Rank would be 10x faster. So exactly as you said. It would be basically a useless power in combat, though I could see uses outside of fighting. Aging a door till it rots, or a steel beam till it rusts or aging a sprout until it grows to full size. You could presumably make a lot of money selling beef cattle?

Edit: Actually thinking about this it still wouldn't be useful out of battle unless the rank number was very high. Like at least Un 100 and that would require significant patience

Perhaps each rank could stack the multiplier?

I suppose if one was willing to do the research and extract info from the comics about supers with aging type powers and then cross reference the actual comic book effect with that super's power rank listed in the reference books... we could then decipher some relevant data to correct it?