I think it depends on your hopes for the future.
I had my first (and only) at 19.
He's 12, he has some additional needs and I split up with his father before he was born.
My whole adult life until now has been dictated by having my son. I've never been able to join a gym, never been able to work too far from home, have had to choose jobs based on location/hours and have passed up some dream jobs. I've missed out on nights out, 18-30 holidays, going to uni and living in halls, and a relationship with a great man who just lived too far away, and so much more. This has all been ok, because I know that my late 30's and my life thereafter will be mine to do as I please.
But starting it all over again? No thanks. I also want a quiet life dictated only by me. Reading books, lie ins, going to the gym, seeing friends, being able to conduct a relationship without worrying about childcare, no resentment about which parent is or isn't doing their fair share, and being able to work late without a second thought, or to get a job with a commute if it's what I really want. Those things will make me happy.
For others, the love of another child would outweigh all those things but it's such a personal choice.