I will start off by saying that I am a proud dad of a 2 year old daughter and I am both proud to be and enjoying raising her. That being said being on this journey is giving me a perspective - I doubt it is anything unique or special, but here it goes.
A lot of people say they are not ready to have kids or not in the right mind/point in their lives. That is completely valid. These justifications usually come because friends/relatives/coworkers start prying and pressuring them into parenthood.
Raising a family is not a right or an obligation - it is neither a given to every individual nor mandated by anyone. It is a privilege that comes with a lot of drawbacks. It completely rewrites a person's life. No one feels ready for parenthood and if there are some mistaken who do they are wrong.
From the finding of a good partner to structuring your life to be stable enough to provide a good environment for a child I make the claim that a big part of himanity is not in a place to be thinking about a family.
Considering how much of an impact there is any reason (whether you see it as valid or not) is a good reason to delay/avoid having kids. The last thing we (collectively as a society) need is another broken family. In that regard you may see that friend of yours as immature or wasting his/her time but the truth is that person has weighed his/her options and decided he/she is either not fit to be a parent or doesn't want to be. Both options are valid and not a reason for judgment.