OP people all over the world have children in “less than ideal” circumstances.
Too young, too old, too poor, too big an age gap between children, too many children already etc etc
The ONLY thing that really matters in the end is will the children be loved and nurtured.
Being older as a parent has upsides as well as downsides. You are likely to be more financially stable and have more life experience/wisdom to offer.
Fundamentally it’s possible to argue that anyone having a child is being selfish. No child asks to be born. We make a decision to have a child based on our desire to procreate, pass on our genes and to be a parent.
Your child will not suffer as you are an older parent and may in fact benefit from it.
In a similar vein (as an only) I get infuriated by the number of people who think I missed out and my parents were selfish (and that I must have been spoiled).
It’s just a silly generalisation people use to a) justify their own choices b) make themselves feel superior (I love being an only btw, was never “spoiled” - wtf does that mean anyway - and have never pined for a sibling).
I think you just need to see it for what it is. Uninformed clap trap and just tell these “friends” to wind their necks in, unless they want you to critique their parenting choices.