Yes as you get older your cycle can be a little erratic. I found I suddenly started to get shorter cycles at around 40... not every cycle but some. I always found that I got pregnant on the cycles where I O'd early. Also as you get older you may find that you don't get as much or seemingly any fertile CM. I had symptoms from around a week after O. So if I O'd on CD11 then I could have symptoms from as early as CD17.... for me it was tiredness, stuffy nose & bleeding gums.