My older son started getting an allowance when he was 5. We stopped for a few months when he showed irresponsibility with the money, and started back up when he seemed to have matured. He gets $1 for each year of age, so he currently gets $7/ week, but will get $8/ week once he turns 8.
He's expected to clean his bedroom and his bathroom when he's asked to, help out with his little brother, let the dog in and out when needed, feed his fish, help keep the rest of the house clean, set and clear the table when requested, take care of his personal hygiene, put his laundry away and put his dirty laundry in the hamper, make and change his bed upon request, and do his homeschool work. He's also expected to generally follow directions, respect people and property, and keep us aware of his location.
He's supposed to check with us before spending his money so we can advise him. He's allowed to spend it on video games, junk food, toys, etc, but we wouldn't let him buy ice cream right before dinner, as an example. And he wouldn't be permitted to purchase things that we believe are inappropriate for him to have (like an R-rated movie).