Yes, it is possible to develop astigmatism if you aren’t born with it, though it is much less likely.
As the eyes grow and mature, their shape can change slightly. Most people with astigmatism are born with eyes that are more egg-shaped (from the front view) than round. It is possible that their eyes can become less egg-shaped over time.
For people born with round, “normal-shaped” eyes, especially for those who have higher degrees of myopia, it’s possible the shape may become less round and more like an egg over time, which can introduce astigmatism.
Astigmatism can also develop due to other eye conditions, an eye injury or after an eye surgery.