The word "youngnesses" may be a bit uncommon, but there are several synonyms that can be used instead. "Youthfulness" is perhaps the most common alternative and refers to the quality or state of being young. "Juvenescence" is another option that refers specifically to the process of becoming young or youthful. "Immaturity" could also be used to convey a similar idea, although it may have a slightly negative connotation. Other synonyms for "youngnesses" include "youth," "freshness," "newness," and "vitality." Depending on the context, any of these alternatives could be used to describe the characteristics or qualities associated with being young.