I had mine at 36 and 39.
I hadn't wanted babies until I met DH and my DSD. We got married on the basis that i didn't want kids. He said that was fine; he already had his daughter.
We used to have her every weekend from about 6 on Fridays until late Sunday evening because her mum worked. I'd never spent any time with kids - career girl all the way. DH worked half days on Saturdays so DSD and I spent time alone.
I gradually learned about children. We played together and I read her stories. She was seven and the most darling child. After a few years I realised that I'd like a child of my own.
So I told DH I'd changed my mind and he just gave me his slow smile. He must have seen it coming.
I'd left it late. We agreed we'd try but if it didn't happen we'd let it go. No IVF etc.
We started trying to conceive at Christmas and I was pregnant by Valentine's Day. It was amazing, and three years later we had our second child.
I would strongly recommend having kids later. I didn't get desperately knackered (though tbh both of mine were chilled out easy sleepers like DH) but I had endless patience and having thoroughly enjoyed my single life I never resented the limits imposed on me by small children.
My relationship with DSD went from strength to strength. I'm a step grandma now. Her DM wanted her to leave school at 16. I had higher hopes for her and my family helped her get her degree financially. In one sense I owe her my babies and she owes me her degree. I feel we're both lucky.