I'm 41 in Feb and have been trying for 6 months for baby no.2. Baby 1 is 17 months now. With her we tried for five consecutive cycles, and I fell pregnant on cycles 1, 2, 3, and 5 (finally with DD). I'm convinced I would've also caught on cycle 4 were it not for a burst ovarian cyst. I was the wrong side of 38 then, 39 when she was born. Now, just over 2 years later, I have regular periods/seem to ovulate regularly but I can't seem to conceive at all.
So my advice would also be don't wait.
Get serious on everything you can do easily now (vits, cut out booze and caffeine, reduce stress, eat healthily etc), and book in asap to see GP. Also, start trying regardless of the state you're in! ;-)
Depending on where you live, you are entitled to a round (or more) of IVF on the NHS, but that will take heaps of time, so like others have said, if you have the funds, I'd skip straight to private fertility testing. Work out first if natural conception/conception by IUI is remotely likely, and if your numbers aren't great/are borderline, move immediately to IVF. Hell, if I were you I would probably just move straight to IVF given the increased risk of miscarriage at our age. There are obviously no guarantees you'll avoid that with IVF, but you'll have a better shot at making sure you implant healthy embryos at least. Start researching clinics, and consider what your max budget is.
I'm off to the GP next week. Expecting nothing more than a pat on the back and a good luck to be honest.🙁Our next step will be whether we want to move to IVF or whether we want to remain forever grateful for our DD and let that be that.