When I was in my late 20s, I also had good chemistry with a female friend who was 32 or 33. She hinted pretty strongly on several occasions that she thought we'd make a good couple. Unfortunately, she had a poor relationship with her father which is a no-go for me due to past bad experiences. I remember she confided in me that she felt like she needed to start looking to date guys in their late 40s/early 50s. She was good looking and a graduate student at Columbia University at the time. A lot of women in their mid 30s who should have very good dating prospects have a lot of stress about being passed over for younger women, and unfortunately they're often not wrong to worry.
If you can't imagine leaving your partner for someone else, and they're worried about being left because they're seeing their friends getting left, words are cheap and your partner will know it. If you can't imagine leaving your partner, then there aren't many downsides to getting married, and your partner will also know this.
Of course, there are others in different situations, but that's the experience of me, my wife, some of my wife's single female friends, and some of my single female friends in their mid-30s. Several of them very pleasant good looking women with graduate degrees from Ivy League schools and good careers.
So, for me, I had gotten a bit tired of the dating scene, really liked my partner, couldn't imagine breaking up, and knew my parter was getting anxious. For us, it was a good move, and has made our relationship much stronger.