Juvenile charged with Agg Assault D/W. Adjudicated and placed on 1 year probation. Is, the now adult, prohibited from possessing firearm?

No. He has never been "convicted" of a crime. He has only been adjudicated as engaging in delinquent conduct.

Only certain juvenile adjudications can be used in adult court and only then for enhancement purposes.

Thanks. That's what I found also. Just thought I would check to see if I had missed something.