I, along with 30 other kids in my grade, took our first algebra class in 7th grade (early 90s). After a few weeks of struggling, I was entirely fine with it. I really think you're underestimating what kids can do if taught properly. If students don't have the "mathematical maturity" for algebra until 8th grade, or later, then that just means instruction in prior years was lacking.

Not everyone took algebra in 7th grade; those who did not, took it in 8th grade.