I hope you don't mind me jumping in (I am going to go and read the other thread). I just wanted to give my perspective, after saying I do think that 23 is not an age to be feeling too old.
I am 24 and TTC #1. BUT my OH is 5 years older than me. We intend to leave a 5 year age gap, so the first one is in school and we have more time for the second one (and the financial side too). If we got pregnant now, DH would be nearly 30 when baby came, 35 before we could start trying for number 2. IF, after those two we decided to have a third and wait another 5 years, he would be 40 and I would be 35.
I know that it is different for men in terms of health, but he wants to be a dad that can keep up. Whilst I am not thinking I am getting old for TTC, I am thinking to the future. I have been to Uni and done my partying. We have been together almost 7 years and married for 2. We are both ready.
It is different for everyone, we all have our reasons.
I mean no harm by this, just a different perspective. Right, now I am off to read the OP.