I feel a similar way. I'm wondering why don't humans gain ANY dex at all from ages 17-20, since wouldn't that be when we're in our prime? (In terms of real life) It's almost as if Nexon was telling Humans, "Be mages and warriors if you plan to free rebirth, but Archery...yeah, you must pay us to be an archer." Seriously, we gain good Int and mana at those ages, which DOES make sense, but still, WHY NO DEX?! *goes to magnum spam Nexon's building*
They had to make some skillset be lower ages, or no one would ever be a lower age thus defeating the purpose. Also, it makes more sense to have higher dexterity at lower ages, you don't get dumber and weaker as you grow older.