Giving the player the ability to customize the MC's age messes around with a lot of things story-wise, so the player does not have this option. For example, the story would play out a lot differently if you were playing as a 40 year old MC, instead of a 23 year old.
I also cannot think of a single otome game where you're allowed to customize age (just that they don't mention age at all). Either way; it's not worth it unless it's a 100% customizable RPG-like game, which Tailor Tales is not.