Long-time readers of this blog will recognize that I have a bit of a complex about being mistaken for a much younger person. I am super-polite (in fact, I'm probably too much of a pushover) most of the time, but if someone dismisses me (or worse, patronizes me) because they think I'm younger/less experienced, I react... poorly.
It pains me to admit it, but there are advantages to looking less experienced when you're working in the field. When I'm trying to fill out resident surveys or asking for permission to access a property, I'm seen as unthreatening. For example, old ladies were somewhat more likely to answer the door to me than to some of my grizzled coworkers.
Also, actively hostile people will tend to attack the person who looks older, even if we're doing the exact same thing (say, collecting groundwater samples from wells on the same street) independently. Not that I can't handle myself, but I'm pretty happy to avoid having an angry neighbor get all in my face.
I guess it's better that I surprise people by being experienced and competent, rather than have folks assume I know what I'm doing and then screw up. But when someone asks if I'm doing surveys for a school project (and no, they're not thinking grad school), it's still incredibly hard to smile and turn the conversation to what I'm actually asking for.