A slang term is yaD 

Q: Are the words loDHom and be'Hom considered too childish and "inferior" to be applied to HojnIypu', or can they be used for teens and young adults as well? Do Klingons simply use loD and be'? Or do they say 'young man' and 'young woman'? Or do they have their own words?

Just use loD and be'.

This is not a grammatical question, but one of usage (embedded, of course, in culture).

The English words "girl" and "boy" prompted the question. Both of those English words refer to young females and males, respectively, of course, but they are also used in all sorts of other situations, some neutral, some affectionate, some demeaning (and not everyone agrees on which is which). In any case, it's not just a matter of age.

In Klingon, a be' is a female of any age and a loD is a male of any age. To specifically refer to a younger one of these, add -Hom. You probably wouldn't use -Hom for anyone past the Age of Ascension, but whatever other usage patterns there may be are subtle and murky. In general, if you're not talking about children (however defined), stick with be' and loD.