How do *you* set and enforce limits for kids of different ages

We just taught our kids that certain privileges come with age. The issue was not equal treatment; it was about the appropriate age to be able to do certain things. Whether it was watching certain TV programs, wearing nylons, getting ears pierced, dating, or whatever, we often allowed our older daughter to do things that her younger sister could not. The younger one just had to wait. It was neither confusing nor unfair. The same rule was being applied to both kids.