What should the age of legal adulthood be?

Please don't say 18, which is still a baby in society. I think a person is truly grown when the brain is finished developing at 25.That's when the brain reaches adult level and society would be better if people did things when their brain are prepared for things.People rushed to adulthood in the past and did things when their brains weren't developed so they messed up society. I feel like the age for adulthood should be 25 or 30. Since the life expectancy is increasing, it wouldn't be bad.