We just started talking about doing an allowance for Luke. I want to pay him $5/week. Like Darcy, he's already expected to do things and help out around the house. I want to start giving him his allowance so he can start saving and learning what it means to save/spend/want something and have no money for it, etc. He will also have opportunity to earn extra money by doing extra things we may ask him to do- like we're landscaping the front yard right now. So if he helps us load up the old rocks/pebbles and haul them out, we'll give him extra.
As far as appropriate for a 12 yo... they look good to me! But I only have experience up to 7 years.