AHH!
I'd really like to tone up my arms because they are quite flubbery compared to the rest of my body so I'd like to balance everything out!
So... I'm going to try the exercise in this video:

http://www.youtube.com/watch?v=P6B6etkU3F8&feature=related

For those who can't see the video, the exercise is basically holding something that is slightly heavy (e.g a 1 litre water bottle), putting it over your head (make sure your arms are parallell to each other) and bending and straightening your arms again. I guess most of you have heard of it.

What I'd like to know is if it would affect your growth (height). My mother tells me to NEVER lift any sort of weight with your arms or else they will become big and your newly made muscles will stop you from growing.

Wow. I don't even know where to begin.

The exercise in question is a standing tricep extension. Its an okay place to start. I've provided a link to another version of the tricep extension that uses dumb bells. Just to give you an idea of a progression:

http://www.exrx.net/WeightExercises/...ingTriExt.html

www.exrx.net is a great site to learn about different muscle groups and how to effectively target them with various exercises. Go explore and have fun.

PS. You won't stunt your growth. Rather, you will grow into the body you were meant to have. :

Oh, mothers.

Maybe this is one of those authoritative-sounding things that mothers come up with when they don't want their child to do something.

My mother used to tell me not to cross my eyes "because they'd stay that way." So far as I know, that is not a good medical explanation for why people actually develop crossed eyes or a "lazy eye" & my mother should know that, since her sister is one such person & has the lifetime of doctor visits, collection of special-lens glasses & medical bills to prove it.

Then again, if I was sassy to my mother, and acting up, and then, a moment later, tripped on the sidewalk & almost fell, my mother would also tell me that my tripping was "God punishing you for talking back to your mother."

OMG I always thought my mom was the only one with the personal vengeful God in her pocket. Yours isn't a Germanic Lutheran by any chance, is she?

Age 67 and she is still on form. I texted her today about my great workout on the rowing machine (a whopping 15 minutes), because all the other cardio machines at the gym were full, and she wrote back that I was overdoing it and would probably hurt myself. I wonder how far Lance Armstrong would have got with this kind of support.

ETA: For the OP, weight training can (in the long run) prevent you from getting short in old age. Resistance exercises stimulate bone growth and increase bone density -- providing you're consuming enough basic calcium -- which builds an important foundation helping to protect you from osteoporosis after menopause. As a college student I was in one of the first studies testing how different types of exercise affected bone density. One semester I was in the control "don't do anything different" group, another semester in the weight training group; there was also a running group. At the end of the study the investigators had a special workshop for us showing weight training was a clear winner among the three. (And telling us please to drink milk instead of soda!)

If I listened to my mother, I'd be wrapped in bubble wrap in front of the TV. It's to the point that I don't tell her my activities until I'm safely back home. Sometimes I don't even tell her at all. She didn't speak to me for 2 days after i went sky diving.