When I was younger I always imagined late 20's to early 30's would be when (if???) I had kids.
Reality - uni, career, travel and the fact that I didn't meet DH until early 30's - and then we weren't in a position to have kids (financially, emotionally, until mid 30s at least.
Then when we did try I had losses and difficulty TTC.
But we had DD1 when I was 38 and DD2 when I was 40. And our next arrivals - well I am now 42 (I prefer to say celebrating the 21st anniversary of my 21st birthday LOL). We would have liked to have #3 earlier, but again we had some difficulties with m/c & TTC, so are just so happy that we have our #3 - and bonus #4! - on the way. But this is definitely it for us.
so in answer to your question - we started TTC when I was 36, had our first at 38, and our last at 42.

just another thought - a friend of mine started her family way younger than me (her oldest is now 17) and she has 3, which she deliberately spaced 5 years apart so that she only had one very small child to deal with at a time (as the oldest was now at school). I like that my kids play together, however, It worked for her, and the older kids are quite responsible with their jobs to help.

whatever works for you and your circumstances really.