We know that human brains are still developing until around 26 years old

this isn't true by the way.

The human brain, particularly the prefrontal cortex, does not reach "full maturity" or "full development at any particular age (e.g. 16, 18, 21, 25, 30). Changes in structure and myelination of gray matter are recorded to continue with relative consistency all throughout life including until death. Different mental abilities peak earlier or later in life.

Text taken from wikipedia's list of common misconceptions. Here's a study on how the brain changes throughout life!