Can an adult develop a lazy eye?

Yes. Lazy eye has many meanings. Lazy eye could be an eye misalignment, it could be a droopy eyelid. It could also be decreased vision from a cataract or refractive error or a retina problem.
No. A lazy eye usually develops during the first three months of life. However early childhood trauma or disease affecting one or both eyes before the age range of 7 to 10 can lead to amblyopia (lazy eye).