Being able to add and subtract money is a good sign - one of my drivers for an allowance was to ward off requests for things in shops: 'Can I get THIS? *brandishes pointless plastic thing*'... 'I don't know, sweetie, can you? How much money have you got? And did you remember to bring it with you?' So the kid needed to understand monetary value, and subtract one from the other.
From memory, this got really solid about age 6. Until around 4 or 5, they typically think that more coins are better, and will choose 4 dimes over a dollar.
I've just hit a new budgeting stage with my teen and pre-teen, and introduced a clothes allowance. The teen gets it as part of a total allowance, to spend as he wishes - if he diligently shops the clothes sales and browses thrift stores, then he has more left over for computer games. This is a monthly amount, auto transferred into his bank account; he's been on a monthly rather than weekly allowance since he was able to get a debit card bank account at 13 (now 15).
The 11 yr old has separate weekly cash allowance (mostly spent almost immediately, on nonsense) and monthly clothes allowance at the moment. She's doing pretty well about budgeting the clothes allowance and understanding that even though it comes in each month (line on my YNAB budget), she needs to roll some of it forward for big annual purchases like a winter coat and boots, and that boring things like underwear need to be planned for alongside funky tops.