It's so nice to hear from other people with the same concerns. I'm 33, finishing up my Masters, and will be starting a PhD in the fall. I definitely started grad school later than I had originally anticipated, but I agree that the additional life experience has been helpful. At the same time, transitioning to grad school after years of working has been something of a challenge.
My main concern is that I'm currently single and would like to find a partner and have children before I'm 40. Dating during my Masters has been challenging, as so much of my time, energy, and focus is on school. The thought of dating, hopefully finding that "right" person, and having children all during a PhD is scary. The thought of not finding that right person and not having children is even scarier. I know navigating grad school while married with kids is hard, but I'm actually envious of those who at least have that part of their life settled.