Permits, food rules, and the parts that need an adult.
Some of this genuinely needs an adult, and it is worth knowing which parts.
Rules vary by state, county, and city, and they usually turn on what the business does rather than how old the owner is. Food is where families most often meet real requirements. Payment apps have age limits. Anything involving a stranger's home, a ladder, or a power tool deserves a conversation before it deserves a customer.
The honest guidance is to check locally rather than trust a general answer, including this one.
Five questions about age, budget, time, and what they actually like doing. Four matched ideas at the end, free.
Take the quizA program from Founder's Best Friend. Built for kids 8 to 18 who want something of their own.