To make an elderly villager young again in VV1, I think it was because of an event!
In VV2, there is something like that when you resolve all the puzzles or almost!

To shorten the amount of time for the farm growing, the only thing to do is to change the speed of the game (in the options)
There is always the same amount of time, in the same speed, between 2 arrivals of crops whatever time you use to the harvesting. And no, watering the crops doesn't change anything!