Many programs set age limits on who they will accept in their programs for partnership with a service dog. Usually I see ages like 12 or 16 as the lower cutoff.
I think that sometimes, especially in desperation, folks can lose sight of the whole equation. Getting a service dog isn't just about what possible benefits might be derived. This decision should be based on a cost-benefit analysis which includes careful consideration not just of the PWD's needs, but also the needs of the animal.
Service animals aren't like wheelchairs. They don't perform consistently no matter who operates them, and they can feel pain, suffer, and die if left unprotected or uncared for. If you forget a wheelchair for a few days or a few weeks, or even years, odds are it will be fine. And even if it isn't, it's just a thing. A service dog is not a thing.
A service animal needs stewardship. That means he needs a handler who is capable of handling him, controlling him, providing for him, and communicating with him.
A service dog handler must be proactive in observing his environment and avoiding pitfalls. See that kid around the corner? The one with the ninja turtles T-shirt who is practicing his karate moves and talking about the "doggie?" If you're a service dog handler, your spidey sense should be tingling. On more than one occasion I've had such children charge my dog with their karate moves.
See that tater tot on the floor? You know your dog has been trained to "leave it" but are you really going to ignore it yourself, or make darned sure your dog hasn't forgotten the rules? Dogs are not machines. Even the best trained, best proofed dog, can AND WILL make mistakes. Mistakes like snarfing that aren't caught immediately damage the dog's training. This is where a lot of service dog teams fail. The human partner is not a dog handler. Perhaps they think the dog is programmable like a VCR and you just "set it and forget it." A good handler learns enough behavior theory to recognize self-reinforcing opportunities like the tater tot and knows how and when to apply reinforcement and correction to maintain their dog's training.
Especially with children, there can be a tendency to think of service dogs as Lassies in capes. Lassie does not exist! She's a fictional character and isn't even a girl or just one dog!!! Dogs are not humans in fur suits. They do not think like humans do. They are dogs, which is wonderful in itself, but we need to be realistic about what dogs are really capable of doing.
A dog has the mentality, the cognitive ability, of a three year old human child. They make the kinds of decisions a three year old child would make, but with dog motivations. Would you send a three year old out to cross the street alone? Would you put a three year old in charge of another child to lead that child across the road?
Service dogs are wonderful helpers. But they are not guardians, they are not nannies, and they are not babysitters. In the human/SD partnership, the human MUST be the adult. If you wouldn't hand off a three year old human child into the care of the would-be SD handler, then please, don't give them a service dog. Not just for the dog's sake, BUT FOR THE SAKE OF THE CHILD.
The handler must make on-the-fly decisions and plans to provide for their SD. I know my dog hasn't pottied in three hours. He had some water about an hour ago and a snack. I'm about to go in to a lecture on thermodynamics. There's a suitable potty area if I deviate slightly and am late for class. Which is better? Walking in late or have to leave in the middle of the lecture when my dog gets desperate? What are the odds my dog can "hold it" comfortably? Do I have a right to make him hold it because of my bad planning? If a kid isn't capable of working through this kind of thought process, then he isn't ready to be responsible for a service dog.
I know there is a popular trend, especially with parents of autistic children to get a service dog knowing the child is not capable of handling it alone, justifying this by saying the parent will be the "backup handler." That's an abuse of the concept of a backup handler. Let's be honest. The parent intends to be the handler. They will be directing the dog and caring for the dog. The parent is using the dog to help them, the parent, to parent their child. The dog isn't working for the child, but for the parent. That isn't a service dog, even if it is helpful. The justification is that they can't handle the child alone and need help. I sympathize, really I do. But a dog should never be responsible for a child like that.
Here's what typically happens. The parent spends a few thousand hard-earned dollars on a miracle service dog that is supposed to solve all their problems of the child wandering or running off, or behaving inappropriately, or demanding the parent's full and undivided attention. The dog arrives and the kid falls in love. At first, there's the honeymoon period driven by hope. Then reality sets in. Now instead of supervising one kid, they are supervising two. Tell the dog to sit. The kid pulls the dog off his feet and he gets up. Or the kid hits him and the parent has to intervene. Now, not only does the parent have to take control of both the dog and the child, if they want to maintain the dog's training, they have to stop right then and there and train. The dog must be proofed, yet again, not to let the kid budge him. Yet the dog is still supposed to listen to and obey the kid at other times. Geesh: how confusing for the dog! Sometimes he's controlling the kid, sometimes the kid is controlling him, and most of the time no-one is really in control.
If a child is not genuinely ready to take on the responsibility of controlling and caring fully for a service dog (100% of the care 100% of the time), then it is too soon. Wait and let the child mature so he can SUCCEED. What can you do in the meanwhile? How about getting a skilled companion dog? You still get many of the benefits with far fewer of the liabilities. A skilled companion dog is usually a dog from a program who for one reason or another is determined not to be suitable for service work. Perhaps he has an allergy that makes him scratch a lot. The dog is still very temperamentally sound (so he should hold up to erratic behavior from children). He's still professionally trained in obedience. He has all the good manners and obedience of a real Lassie. He's a great buddy for the kid, a buddy who attracts other children and makes the disabled child "cool." He's still someone to hug, and sleep with, and he still has fur to cry into when the child is frustrated or hurt. The difference is that a skilled companion stays at home (or goes places with the family where pet dogs would ordinarily go). There's no juggling of leash, dog and child unless YOU the parent choose it.
One last thing to consider: after the child has heard wonderful stories of magical service dogs, and he gets his very own magical service dog who loves him and whom he loves, and he takes it everywhere.....can you go back? Can you suddenly say, "this really isn't working out the way I planned, Fido needs to stay at home because I just can't handle it all." How is the child going to take it? How can you explain?
PLEASE PLEASE PLEASE consider very carefully before seeking a service dog for a child. There are so many pitfalls.