While it's good to prepare for the future, she's not wrong. Once your youth is gone, you're not getting it back. No use having a master's degree and a prestigious 6 figure a year job if you're alone and childless at 40+, and all the good guys / gals you had an opportunity to get together with got snatched up by other people who were living in the moment 10 years ago.
Edit: Also, I'm glad I'm not the only one thinking that the logical end / continuation to this series would involve the girl getting pregnant, a hasty weeding, and a new titles featuring how they're teenage pregnant and such. Although to be fair, in the past, having a kid before 20 was normal. It's only the last several decades where marriage and kids were delayed so late.