Well, if lots of people are delaying pregnancy as you describe then you won’t be the only only mum!
I’m an old mum to my ds2; I was 42 and dh was 40.
My mum was 40 when she had me and my dad was 41. I remember them dragging me on mountain-climbing holidays when I was 15 so I knew first hand that old parents don’t have to be indolent parents. My parents were constantly active and exciting to be around.
I do think a lot of it is about circumstances, health and attitude. Dh and I work hard to keep fit and active and eat healthily. Right now my dh is out on a 75 min bike ride with ds2. We also work hard to be financially secure so if we die young, our kids are fully provided for.
My pregnancy with ds2 was textbook perfect. I started long walks 7 days after he was born and was walking 5 miles every weekday by the time he was two weeks old. By the time ds was two, we’d often spend a few hours a day out walking and playing at the park or on his balance bike or digging in the garden.
I am not going to say it’s easy - of course we might get cancer or heart disease and of course statistically we are unlikely to be alive if our own kids have families later in life too. I am sad that my dad never met either of my kids. But only just earlier today my son told me he’s going to grow up to be an engineer just like my dad (probably true - ds is very good at practical STEM stuff).
But parenting always has its challenges and I don’t regret having my second child so much later in life. Dh and I have a much stronger marriage now than we had ten years earlier. We provide a happy, comfortable home for our son. We aren’t obviously as energetic as we were in our 20s and 30s but we still have a spirit of adventure and we like new challenges.
And I don’t feel ostracised at the school gates. I’ve been welcomed - I don’t have lots and lots of mum-friends age 30 as of course lives are very different. But I’ve got a few around that age. We learn from each other, in the same way I have friends from different cultures. Age is less of a barrier when you’re an adult.