Usually starts when they're 30-32.....they realize the biological clock is counting down fast and "35" seems to be the magic age. They're a strong independent woman......and realize they'll likely be "independent" at 70, unless you count cats.
Rather than letting a relationship run its course and grow into a stable partnership, and lead to marriage - it's suddenly 'don't waste my time,' I'm in it for marriage (meaning they want you to be prepared to agree to sign over 50%+ of your s4!t a couple months into to dating).
They can't understand why a guy would be hesitant to accept this, and be more interested in a girl 10 years younger, without the useless studies degrees, and whatever "career" she slept her way through for promotion.
I believe the guys understand the child is the primary goal of some of those women - not a stable family/good marriage. The guys should be wary...