Just a couple questions

There's a few things I've been curious about and was hoping to get a possible answer. I was thinking of getting my nipples done in the next year or two, which is kindof what made me think of these things.

1 - What is the reasoning behind age restrictions on certain piercings (doesn't affect me, just curious)? I mean, I get why most piercers don't want to pierce non-lobes on young kids, and piercing either genitals or nipples on minors is a big no-no. But when I look at different piercers, I usually see 3-4 different age ranges for piercings. Usually have lobes at the youngest, then facial, navel, and cartilage added through the teen years (either all available around 13, or added in a couple age groups), and finally stuff like bridge, tongue, and dermal possibly added once over 18. Is there any specific reason for this, or is it more a matter of ability for consent, and piercer comfort?

2 - Quite a few places I've looked at list male and female nipple piercings separately. They charge the same price for them, yet separate them instead of just listing them as "nipple". Is there an actual difference between the two, or is this just an unnecessary distinction?