Hey, if you just want to go out there and do it... then do it.
I know with duathlons... really good runners and cyclists tend to be drawn the to the events. Whereas at tri's, you see more a large range of fitness levels.
But if you just care about enjoying the experience... and being there... and having fun... then go for it.
I also encourage you to start going BRICK workouts right now. Do bike/run/bike/run workouts. It can be short distances, but you need to get use to the jello legs when you go from bike to run.
GOOD LUCK!
"Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather, to skid in broadside thoroughly used-up, totally worn out, and loudly proclaiming: WOW WHAT A RIDE!!!!"