What term describes when a young animal becomes capable of successful reproduction?

The answer is puberty and maturation. In this stage of reproduction the fertilization occurs in which new development of an organism arises.  It simply means the birth of new specie and this is where animals became capable of successful reproduction.

the electromagnetic spectrum includes, from longest wavelength to shortest: radio waves, microwaves, infrared, optical, ultraviolet, x-rays, and gamma-rays.