Maybe it's that it's more expensive to do a startup as an older person (your time is more valuable since you've built up more skills, for example), so as a resu

Maybe it's that it's more expensive to do a startup as an older person (your time is more valuable since you've built up more skills, for example), so as a result startups that are founded by older people are the ones with unusually strong premises or reasons for being. It could be a selection effect.