When he was partway through the process I read a book that suggested that Scouts should get their Eagles before they entered high school. That's a BIT ambitious, but I'd think by the time they're done with 10th grade would be a good idea. That's usually before varsity sports, driver's licenses and dating get going and they lose focus.
We tell parents that they have to work and be involved in Scouts with their son. That's because the three deadly sins will come along to keep him from making Eagle if they are not active.
Oh the three deadly sins, what are they?
Girls
Cars
and a Job to support the first two.