Curves accepts over 12, with your mom's permission. As stated, you could even get your mom to join with you. It is "generally" $29/mo...plus startup fee, per person. The monthly fee can vary just by a few bucks. IE: I've always paid $29, until my new location...which charges tax on memberships in their state. So now I pay $31 something. The startup fee can vary from $0 to $150. I got in on a half price special and paid $75. My mom joined a new Curves looking to build a membership, and so they waived the fee entirely.
Curves is a circuit of equipment that uses hydraulics. The faster you work the equipment, the harder it gets. New Curves usually start with 8 machines, but there are a total of 13...plus a stepper that replaces one of the recovery stations. If you have 13, you go around the circuit twice...to get about 30 minutes of exercise. We have 8 at our location and go around 3 times. My mom's location has 10 and goes around 2.5 times.
You get 30 seconds on each station. The stations are set so you do something to work one muscle group for 30 seconds, then you move to the next station which will be a recovery station. That means you can either stand, walk in place, jog, jumping jacks, dance, whatever. If your heart rate is too fast, you would stand and let it level out. If it's not fast enough, you might want to move around a bit. After 30 seconds of that, you move to the next station, which will be a machine that will work a different muscle group.
Check out
www.curves.com. You can use one of the special promotions and try it out for 2 weeks:
http://www.curves.com/about_curves/sponsorship.php
To get a glimpse of the type of equipment they use:
http://www.curves.com/curves_right/thirty_minute.php