Answering my own question
I went through Confirmation as a Catholic at the end of 8th grade. I was one of the youngest in my class, so I was still 12. At the time, I was starting to doubt whether I really wanted to be Catholic. If it had been up to me, I would have asked to put it off for a year or two until I'd sorted some things through, and most likely never would have done it. But it was quite clear to me that if I wanted a roof over my head, I was getting confirmed on schedule.
Judaism is a little different. You become bar or bat mitzvah at age 13 (12 for Orthodox girls). You are then considered an adult - whether or not you participate in a bat/bat mitzvah ceremony, chant from the Torah, and have a big expensive party afterwards. (In fact, the idea of a bat mitzvah ceremony for a girl is fairly new.)
There is also a confirmation, which in my congregation happens in 10th grade. To be confirmed, you have to continue studying over and above the requirements for a bar/bat mitzvah ceremony. But being confirmed is the exception rather than the rule.
The problem is that the age of adulthood in many faiths was set back when 12 and 13 year olds could and did go off and get married and set up their own households. Nowadays, our culture and laws consider you a child until you're 18. I think you have to make a decision like confirmation of your own free will, and if you're going to be stuck as a child in your parents' house for the next five years, you don't really have that freedom.
My hypothetical future children will be going to Sunday school and Hebrew school, but if they then decide they don't want a bar/bat mitzvah ceremony or to continue studying and be confirmed, that's their decision and I'll respect it (although I will be disappointed).