Every boylover uses this term differently. Some reserve the term for the boys they have close, ongoing friendship with, and others use it more liberally to describe any boy they have contact with. To avoid this ambiguity the variant special young friend is sometimes used to refer to a close friend. Neither term carries any sexual connotation.
Many boylovers continue to consider a person his young friend long after the boy has grown into a man.
The term "young friend" evolved as a play on the terms boyfriend and girlfriend and is usually abbreviated as yf (or syf for "special young friend") in writing. Online, it has mostly replaced the older term boy because many felt the phrase "my boy" sounded more possessive than "my young friend."