There's no such thing as an adolescent silverback. A silverback is a fully mature dominant male. They don't gain the silver coloration until they are mature, so the entire premise is a contradiction in terms.
The Wikipedia article makes exactly one reference to silverbacks, again referring to the leader of the troop. Do the world a favor, check yourself before you talk shit.
I looked it up at first and the phrasings I kept seeing was "species of mountain gorilla" so I assumed that meant it was a specific species. Woke up to the downvotes so I looked a little deeper and found out I was wrong.
Personally I blame Google for not being able to answer concise questions like "is a silverback gorilla a species" but it is what it is ¯\_(ツ)_/¯