There's no way around it, people will always initially judge you by their first impression of you. So, make that first impression as polished and professional as possible. This will give you the opportunity to hold them long enough to hear what you have to say. Once you do speak, avoid youthful slang and make strong eye contact. Beyond that, don't overcompensate, just remain professional and demonstrate a positive, upbeat attitude.
The woman at the head of the U.S. home decor empire and the man at the head of the gigantic Chinese ecommerce platform have risen to become titans of business by bowing at the altar of the middle class.