coin age should be set to about 8 hours.

There is no such thing as stopping the staking. New coins you get after staking have to go through the minimum coin age as well, but they never "expire" per se. You can stake unlimited on same amount of initial coins.

Yes any potcoin from day 1 is eligible for staking.

The software needs to download the entire chain, that could take a while. We will create an updated "bootstrap" to accelerate things, but that is more for advanced users.

hope this answers your questions