Can a young person (20s) have IOL surgery if they are not a good candidate for laser eye surgery?
If by "IOL surgery" you mean the removal and replacement of your natural lens with a cataract-type intraocular lens, the answer is a VERY tentative "Yes." There are many reasons NOT to do this at your age. The quality of vision under different lighting conditions is NOT the same with any of the available IOLs as compared to the type of natural vision a person born with healthy eyes and no refractive problem (needing glasses) has. While IOL technology has advanced tremendously in recent years, there is still no IOL that can provide the same level of rapid accommodation (shifting to near focus), lack of internal reflectivity, and non-sensitivity to glare and optical distortions under reduced lighting conditions.
If you are myopic (nearsighted), with or without astigmatism and not a good LASIK candidate, there is the ICL (Intraocular Collamer Lens). This type of implantable lens does not require the removal of your own, natural lens and is reversible. Technically I suppose this is an IOL, but eye doctors consider it in a different category than the IOLs used in cataract surgery.
There are some conditions where an IOL could be a reasonable and relatively safe way to achieve good vision without glasses in a 20 year old, but they are quite rare.