Is it appropriate for a bishop to ask for the congregation to sustain a young 12 year old that is going to be ordained to the priesthood
Thank you for your question. Not only is this appropriate for a Bishop or one of his counselors, but they are actually instructed to do it. Sustainings to the Aaronic Priesthood happen during sacrament meeting, while the ordinations take place outside of that meeting, typically in quorums. The need to sustain potential deacons from the pulpit is further explained in D&C 20:65 where we read:
No person is to be ordained to any office in this church, where there is a regularly organized branch of the same, without the vote of that church;
Similar to sustaining a soon to be new deacon, we in turn also sustain our church leaders, including our Bishops. We sustain them as they try to do their best in their calling, helping to lift their burdens and make their yoke lighter as they volunteer their time to serve us. Church leaders are not perfect, but neither are we, thus we should be encouraged to help lift one another in love and avoid any unnecessary fault finding.
Thank you again Doug,
p.s. For additional information: Chart of Callings