I think this kind of thinking is normal sometimes, especially if you are unhappy with an element of your own life - it's easy to measure others by your perceived deficits. I used to indulge in this a lot until a kind (but blunt!) friend told me I was being needy and boring!
If you are unhappy with some aspect of your life, focus on changing that. Stop dwelling on what others do or dont have, no ones life is ever "perfect". I think it's also worth noting (and I mean this kindly) that when you become a parent you surround yourself with other parents and measure yourself against them - which is perfectly fine, but I think there is a risk that you become a bit myopic to the fact there is a whole range of other lives and lifestyles out there.
I'm the same age as you so I came back to this thread after doing a bit of a mental inventory of my closest friends. I realised that while I am envious of some aspects of of their lives, I definitely wouldnt want to be any of them completely! We all have our own struggles. For illustration here's a round up:
Me: married, desirable career that I love but mediocre pay, no kids atm (both choice and circumstance, I will be happy with either path), renting. The fact that we dont own a house really bothers me but I'm doing everything in my power to change it.
Friend 1: married, 3 kids, sahp, home owner, lives a very frugal life, sometimes takes "little jobs" for extra money. Shes very good at being content but has voiced frustration at lack of money.
Friend 2: single, rents in house share but could buy, good career. Really wants marriage and kids.
Friend 3: no kids, newly divorced, home owner, just took massive pay cut to change career. Shes shaking up her life to go for what she wants.
Friend 4: married, 2 kids, sahp, home owner, high earning partner. She has a "hobby buisness" that doesnt really earn (her words not mine), she sometimes feels a bit down about lack of real career but appreciates shes lucky.
Friend 5: serious relationship, no kids, high earning desirable creative career, has never moved out of parents house. Now looking to buy with partner.
Friend 6: married, 2 kids, home owner, part time career. Loves job and wants to stay in sector but is always stressed out and torn between job and parenting.
Not sure if that's at all helpful, but it certainly puts things in perspective for me. We're all just living our own lives.