Treating people who are grownups like grownups is a good thing to do. Seriously. People like to be respected I have discovered. Talking down to someone is not right. Most people are very capable and mature and want to be treated as such.
If you are older respect people who are younger with the same level of respect you give your peers. If you are younger honor the life contributions and experience of older folks.
Don’t let your first impression be the only thing that informs your long term opinions about something or someone.