I am 22, at University and single. I have no aspirations to be a mother anytime soon. Washing, feeding and clothing myself seems enough of a challenge at times, let alone having that responsibility for another person. But perhaps surprisingly to some, the age at which people are planning to have children is something that is discussed. No one is making a big song and dance about it, (no one wants to seem crazy) but spend a few minutes with someone 1:1 you find that this is something that most have at least thought about (or the girls anyway..)
I am a medical student and most medics I know, like me, like to plan ahead. They know where the next few years of their life are going. Get to the end of medical school, and then foundation year 1, foundation year 2, choose a speciality and then work to be a consultant or become a general practitioner. So why wouldn’t you at least think about the other side of your future (the non-academic /family side); this for a lot of people includes having children.
I remember talking to a friend after they finished at University and moved to the city for work. “I need to find a guy now and settle down”. This was at age 21. To me this seems ridiculous because it was clear that this wasn’t really what they wanted, they were just ticking boxes. Got the degree, got the job, now need a man, a ring and some babies!
Assuming that you have met someone you would like to have children with (a challenge in itself), at age 21, apart from getting help from the bank of mum and dad (not ideal) straight out of University your bank balance won’t be fantastic. I don’t know how much junior doctors earn but with students loans to pay back, bills, rent, additional costs (council tax -_-) etc it is fair to say that it will be a few years before most medics and indeed graduates will be in a financial position to start a family. Therefore you could easily be in your 30’s by the time you are even in a position to consider it.
Not to say that this is a total disaster, but trying to start a family later on in life brings its own problem. The biological one. (The alternative, have your children young, is the difficulty of juggling a demanding career at the same time. Again not easy.)
I personally blame our body’s inability to adapt quickly enough to the fact that our lives have changed so much! Graduating, getting a job, finding a partner and financial stability all take time, for most of us all of our 20’s. Unfortunately, our bodies haven’t adapted quickly enough to keep up with the change.
In my case, I will be at University for 3 years longer than the average student and will therefore enter the job market 3 years later. So I am already ‘behind’. I will leave University at age 24 and then be working as a junior doctor for 2 years and then I will be applying for speciality training, this doesn’t seem like the ideal time to be thinking about having children…BUT if I wait until I am consultant, I might be risking my fertility and if I have children before becoming a consultant then I risk my career. Catch 22!
I know I have painted quite a bleak picture but this wasn’t my intention. These musings are just based on discussions I have had with other people in the same boat as me (young graduates or fellow medical students) and from seeing and talking to female doctors. In reality I don’t see many women who by my definition who ‘have it all’. I know that there are exceptions to this. I’m sure that someone knows someone who has 8 children, is a neurosurgeon, a vegetarian, does charity work on their summer holiday and looks like Meredith Grey. But in the real world, I see 50:50 or 100:0. By which I mean work is ok family is ok, but neither are great. Or work great, family none existent or family great and work none existent. I want 100:100 but I have yet to figure out how to achieve this and I don’t think I’m the only one… 
 I mean people really doing whatever job they want to do and being happy in that field, not making a compromise because it ‘fitted in with family life’ and have a great family life too.