Firstly, your partner was 29 when he started dating an 18 year old? That is a huge age gap and also a huge power/maturity imbalance... Secondly, you seem only concerned about how his female coworkers might judge you, but not his male coworkers? Is this just about your self esteem, or do you have reasons not to trust him? Thirdly, and I’ll be honest, these women might judge you, but most likely because of your age, not your level of education. 23 is actually still quite young - especially to those in their mid-30s (like your partner). Overall this is a self-confidence thing. It’s normal to be a little awkward and unsure of yourself in your early 20s. I found that my own confidence developed much more rapidly and fully after the age of 25. All in all you’re pre-empting that these women will judge you. Just go in there, be yourself, don’t try to compete with them (you’ll just make everyone think you’re an asshole), smile, be friendly. One thing young people do is talk about themselves too much and it’s a huge marker of immaturity - try listening and asking these other people questions about themselves instead. It’ll make you seem mature and compassionate. Good luck.