In many Shuls they let a boy younger than Bar Mitzvah do Gelilla. It makes the boy feel like a part of the Shul and encourages them to participate. When this is done a few things should be considered…
1) Is it a large Torah scroll that will be above the reach of the boy to roll and put on the mantle?
2) If the one honored with Hagbah needs help can the boy help and if not, the gabbai or someone needs to be there to assist.
3) It should be explained to the boy not to touch the the klaf and if it slides while rolling to lift it with the gartel.
4) Is it a relative novice doing Hagbah, he might need more help than a boy can provide.
5) Remember that gelilla is an honor to receive and that even in Shuls that do give it to children Men should not be excluded from receiving it.