Hello and welcome to MedHelp's forums. Ability to conceive does indeed decline with age. With no other factors alone, women as they advance in age and particularly past forty will have a decline in fertility. https://www.acog.org/Clinical-Guidance-and-Publications/Committee-Opinions/Committee-on-Gynecologic-Practice/Female-Age-Related-Fertility-Decline. Even when desiring pregnancy and using assisted reproductive technology or ART, the statistic for actual live births is very low.
However, it is not a complete impossibility. Your irregular cycle complicates matters further. Here is some information on taking a pregnancy test https://www.webmd.com/baby/guide/pregnancy-tests#1. You should be able to take a test for accuracy 21 days after you had intercourse.