I replied that I thought it was ridiculous to pick an arbitrary age and think that is the magic bullet.
I married around the age of 30 and I think I have a pretty good marriage so you might think the bitter divorcee advice holds true. But I dont' think it was just our age that made it so. I think it was the fact that he was available as often as I wanted him to be. He didn't weasel out of dates or show up late or not show up at all. He cared about my well being (in the bedroom, even). He valued me as a friend and as a person with thoughts and opinions that mattered.
Not exactly advice on marriage but a good parallel, I read an article by a therapist who suggested we teach our daughters to only have sex with someone who feels like a best friend, who acts like a best friend. Someone who you can talk to about anything, who you trust will stand by your side, who helps you when you need it, who is reliable, who shows up, who is kind in words and actions. Most of our kids know what a best friend looks like so it's tapping knowledge and feelings they're already familiar with.
What kind of advice would you give someone who wants to know the secret to choosing a healthy mate?