I'm a massive body modification enthusiast. I know ALOT about piercings, just from years of being pierced and being interested in the art.
The legal age to get a piercing (in QLD anyways, might want to check your particular states legislation) is 16, and 18 for anything near the female or male genitalia.
At the moment i only have 4 piercings; My septum (often referred to as the 'bull ring') Both my ears are stretched to 1.5cm & i have dermal anchor piercings in my wrists. I also previously had surface piercings on my collar bones, snake bites, angel bites (dumb name. like snake bites but on the top lip. as well as the webbing in between my top lip & gums (a small ball & ring hung in front of my smile. sounds weird. looks great!)
Ok. Now i have to stress. DO NOT GO TO PLACES LIKE HAIR HOUSE WAREHOUSE OR PRICE ATTACK!
These places DO NOT hire properly trained piercers, yes majority of them have done a piercing course, but that does not make them qualified.
Go to an actual piercing shop. Do not go to a hair supply shop to get a piercing, you will honestly regret it. A piercing shop is more expensive, but you're paying for quality work, jewelry not to mention the aftercare. If you do have issues with new piercings, places like Hair Warehouse do not provide adequate information let alone help. A good reputable piercing shop will always see you regarding you piercings and their health, and they know exactly what they're talking about.
As far as general aftercare of piercings goes. You can purchase the cleaning sprays they sell at Piercing shops, but its also just as good, if not better IMO to use salt water. Just a matter of dissolving sea salt (make sure its sea salt not cooking salt) then letting it cool before soaking your piercing. you should do this regularly, about once of twice a day for the first two weeks.
Don't be fooled. piercings do scar, it just depends on the placement, the quality of the piercing job and the persons skin, as well as the length of time you keep them in for. For example, i have scars from my snake bites which i had pierced for 5 years, but not from my angel bites as i only had them a couple years.
Piercers DO NOT use numbing gel. Even tattooists don't use numbing cremes, they're expensive and not readily available here. Plus, you seriously do not even need it. Your ears will hurt for a second, then just feel hot. Your lip will hurt too, but only for a short amount of time. then it'll be a little swollen for a day or two and a little sore to the touch. But nothing unbearable at all. If you're looking to avoid pain, avoid surface piercings and tattoos. lol.
Ah. teeth. Yes, piercings do effect your teeth. It does depend on the mouth and the piercing placement, but it is very rare that you won't do any damage at all. Most people get tiny fractures in their teeth, chips, or their gums can recede.
Hope i helped, some answers may not be what you were expecting, or wanting, but its best to be informed and be able to enjoy piercings without any surprises down the track.
Be warned, piercings can be like tattoos, once you get one you just need more. I'm already up to no.27 & counting... haha.
feel free to ask me anything else if you're still wondering =P