The answer to this is far less complicated than it seems:
By the time you are 30, you have fully developed into who you will be and you are far less likely to make drastic personality changes.
In other words, in your 30’s, you are who you are! I often tell 20 somethings that they shouldn’t get married before 27 because the human brain is not fully formed until the late 20’s. I stand by that advice, but I also think there is something we can learn for our 20 something ways of being.
In your 20’s you are taking the time to figure out who you are and because you are still trying to gather all the information, you are more open to new and different ideas, people, living situations, etc. You’re just more flexible. In my 20’s, I was in long term relationships with men that I saw no future with but just enjoyed the moment and the stability. In my 30’s I would never dream of starting a relationship with man unless I saw significant signs of future compatibility.
In our 30’s we have become far too self centered and focus too much on having the life and the partner we designed in our minds. This is especially true of singles who had thrived in their careers in their 20’s. By the time you’re 30’s you think, “I achieved what I wanted to in my career by making goals and sticking to them.” They often transfer the same mindset when it comes to relationships, but unfortunately, that’s not how love works. Trust me, I know because I have tried that approached, and tried, and then tried again. Making a list and checking it twice is not the way. Ironically, I’ve actually dated men who have checked almost every box on my list, but sadly the chemistry was missing.
This is disappointing news for the types A’s out there because there’s no planning when it comes to love. True love is amazing! It’s rare. It’s random. It’s unpredictable. It’s unplanned. You can’t say “I’ll fall in love after grad school and before I make partner.” The best thing you can do is to go back to your 20’s mindset and be open. The one you end up loving may be a different race, class, profession, or religion than one you imagined and that’s perfect okay.