How old were you when you started?

Hello all,
I'm 31 (m) and my wife is 30.
We live in a happy marriage for 4 years already (together for 9). I had a fantasy for years now about including another man in our sex life, she wasn't particularly against it, but she also didn't seem too enthusiastic. Now we are at the beautiful stage of our life where we are becoming parents pretty soon. Since we want more kids, our life is going to be all about them in the upcoming years and I'm a bit afraid that my chance to fulfill this fantasy has passed.

Can you give me your experiences? Is my situation "normal", can I be hopeful that we can still experience these kind of things in our 40s?
Question to the women here: did you have a big turnaround about this topic in your life or you were always into this extra "attention" from men? My wife has only been with 4 guys total (me included), so she's not letting her "slutty" side out easily.

Thanks for you input in advance🙂