Answer:
Never ahead, ever behind, yet flying swiftly past, for a child, I last forever, for adults, I'm gone too fast.
Light me up in backyard gatherings
I help engines spin and pants stay up
I am lighter than air but a hundred people cannot lift me. Careful! I am fragile!
I am commonly ate before I'm born and after I'm dead.
Nothing specific, but more than a few. This many clustered, together will do.