Just a few quick tips from experience for you - because we didn't get into a design field to get a 9-5 or wear a suit - but the people who are our clients operate that way, so sometimes we gotta get dirty.
It's all about relationships. For the past 9 years, I'm always the youngest guy in the room (w/ responsibility, not talking coffee assistants). No matter how much I (you) know, how talented I(you) am - I'm usually sitting in a room w/ groups of 40-60 y.o. men w/ a lot of money & field specific power. So the tips I'm giving today are based on how I got them to respect me in the 1st place, as well as develop our relationship.
The head of a major international Mechanical Engineering firm tried to put me to the fire in an early meeting. I happened to point out an obscure piece of building code he wasn't aware of - at first it was easy to shrug me off due to my age - but after review I was rewarded w/ credibility. This same engineer - when I had a large condo project a few years later - I called him - knowing that his services are upward of 100k, but it was worth it as we had developed a mutual respect. When I met w/ him to discuss the project and his fees, he told me he would do the job for (honestly, I can't even say) - with his reasoning being that liked my business attitude & demeanor, he trusted me, and because he, 'want(ed) to support up & coming designers.'
Or how bout the vice principal of ____, whose apartment briefly held the title of, 'tallest residential space in the world,' calling ME up - to invite my old boss & team on his yacht for a catered event. Or international designers (London, Japan) calling me for NY regulated consultation? Or when the office moved & many of our outside associates sent me gifts, including a tree, a nice bottle & other things - while my bosses got nothing.... How did I gain such credibility so young? Few simple things, here they are:
1)Keep your mouth shut. Remember the people you are dealing w/ are not as knowledgeable about your services are you are - so trying to dazzle them w/ terminology and jargon either loses them, confuses them, or both. Most often they -understand a certain phrase & you waste an hour explaining it to them. You can't put your foot in your mouth, if it's shut.
2)Be knowledgeable. You worked hard to get here - you got your education, your degrees, your work experience , your confidence - LET THAT SHOW when you speak - speak confidently. If you haven't been putting your foot in your mouth - when you do speak it holds more weight. People respect one good idea an hour as opposed to trying to force your way into every decision that needs to be made & you end up looking like a fool that shouldn't be there. After all - you worked hard to get there, no?
3) NEVER say 'I don't know.' Say it to your friends, your mother, whoever the fuck - NEVER NEVER say it in a business meeting. Again - fall back on your credentials. One thing I know about myself - after this many years if I don't know something myself, I know I can get the information w/in 24 hours from wherever it may be. So NEVER say, 'I don't know' - because what everyone will hear is, 'I don't deserve to be here.' When the occasion comes up that I really don't know something, I have a few go-to phrases. 'You know, that sounds familiar/We did that on a job a few years ago/He's my mother,' all can end in - Let me check my files at the office & I'll get back to you on that.' If there's a lot going on: 'Let's list it as an open item, move on, and I'll get back to you when I have the info in front of me.' Smart people know it's worth it to get the facts straight anyway....
3 Simple things. Actually, if you're always saying, 'uhm,' - STOP THAT. I learned that in 8th grade English Mrs. nightmare mode - you should know that by now. Be quiet, Be knowledgeable, Be Confident - no matter what your age these old heads of companies (they still rule the world as of now) will respect & listen to you.
And be friendly - that's another non-tip-tip - don't be the young dickhead that looks like he's out for higher up jobs. People can see that a mile away. Speak authoritatively, yet friendly.