I agree with your last paragraph and I'm so glad that many are shunning the age thing being used as a yardstick to measure maturity.
Some elders still behave childishly and irresponsibly causing me to roll my eyes in disgust.
Your bro is a genius child, he was already mature from the womb, you guys just didn't know it.
While some individuals may not exhibit the expected level of maturity regardless of age, it's important to recognize and appreciate maturity wherever it may be found.
Thank you so much for reading, girl
You're welcome