1. 16 in a reputable place, most places would probably do it maybe with a parent/guardian there if you didnt have any proof of age.
2. i had mine done about 2/3 weeks ago, and the swelling went down in around 4/5 days, you cant talk properly for the first two days, and cant eat properly at all for the first few days (soft food only), i went back to get the bar changed after just over a week, and i couldnt eat properly until then because when i tried to eat normal i bit really hard on the bar and that hurt like hell!!! you need to swish your mouth out with salt water twice a day, and then on top of that swish it after any food/drink you have thats not water. i havent had any trouble with mine getting infected or anything.
3. about the same as getting your belly button pierced, depends on how high your pain threshold is i suppose. mine didnt hurt that much, it didnt hurt half as much as a thought it would! until the swelling goes right down and the bar gets changed to a smaller one its more awkward than anything because you cant eat properly if at all! once the bar gets changed its fine - or it should be.
i will say though that i think the most painful bit was getting the bar changed.
i hope this helps, and let us know if it goes okay. good luck!