Can a seborrheic keratosis slowly grow over a number of years?

Yes: Yes because Seborrheic keratoses do not go away on their own, but they can be removed if they become unsightly. There is no poblem in not treating the growths, because they are benign (noncancerous) and do not become cancerous.Seborrheic keratoses grow slowly, in groups or singly. Most people will develop at least one seborrheic keratosis during their lifetime.