I let my 8 (now 10) year old stay awake, on the condition that
1. He sleeps for at least 3 hours Erev Shavuos
2: He knows in advance what he wants to learn
3: For at least the beginning of the night, he has someone to learn with (at least 45 minutes)
4: If he gets “bored” he has books to read to keep him busy
5: I dont have to carry him home from shul in the morning.
He stayed awake the entire night, last year, learned for about 2.5 hours and didnt bother anyone in the shul.