There’s no age limit on picking up a pen. Grandmas publish first novels. Teens drop platinum tracks.

The idea that there is a window for starting comes from watching a small number of visible careers and mistaking them for a rule. In practice people begin at every age and always have. What looks like a closed door is usually the absence of anyone your age among the examples you happen to have seen.

If you have been carrying a private sense of being too late or too early, check whether anything concrete supports it. Start at the size available to you now, and let the calendar stay out of the decision.