Not sure I see it that way.
I think you’re positing that people would stay not only ‘young’, but also ‘immature’, for their entire lives. Since we reach full intellectual maturity at around 25, it doesn’t follow that we would necessarily be old but youthful immature people.
Moreover, it seems common that older folks, realizing their time is short, have a greater propensity to turn to God and amend their lives. If folks generally retained their youth but realized their time was short… don’t you think they’d amend their lives, too?