You can enter your local triathlon or duathlon and probably do quite well if you’ve trained a bit. But how good are you?
If you entered a BTF Age Group qualifier event then you would be up against, typically, serious athletes (or at least people who think they are serious). You might not do so well. But at the larger events then you can get a good grasp about where you stand across a spectrum of abilities. The guys/girls that win your age groups will almost certainly be great athletes and if you are better than 120% of their time then you could think about what you could achieve with a bit more focussed training moving forwards into 2016.