I know age affects stats, however - if someone rolls a PC at an age that is younger than their 'peak' giving them slightly lower stats - do the stats rise as they grow? do they 'grow' out of it as they reach their peak age?
Yes. Strength and endurance rise until you reach your prime, and then decline. Wisdom continually rises, and agility continually drops.
Note that because score is more of a rough estimation of your attributes (it gives you a category, within which is a broad range) you won't always actually see your stats change as you age, but they do.
Strength and endurance seem to drop and drop as you get the other side of middle age. :(
Yeah, it seems a bit extreme.