I think as they get older, it becomes easier for them to do lots of things at once, especially if the academic challenge isn't quit up to snuff. By the time my son is 10 or so, I expect to follow his lead more than I do now, and if he chooses to be what I would consider to be overprogrammed, then I'll be a lot more okay with that than I would be with a 3-4-5-6-7yo child.
But I tend to think that the younger they are, the more downtime they need to think and dream and play and process the day's input, even for the highly outgoing, on-the-move kids. But since all kids are different, naturally YMMV, and you have to do whatever works best for your particular child.
