A lover of something.

A person attached to a particular pursuit, study, or science as to music or painting; especially one who cultivates any study or art, from taste or attachment, without pursuing it professionally.

"The contest is only open to amateurs."

Someone who is unqualified or insufficiently skillful.

"The entire thing was built by some amateurs with screwdrivers and plywood."

Non-professional.

Created, done, or populated by amateurs or non-professionals.

"amateur sports"

Showing a lack of professionalism, experience or talent.

"Duct tape is a sure sign of amateur workmanship."