I did the senior games 5K TT qualifier in 2009. There is a wide range of abilities in each age group from seasoned, accomplished USCF racers to recreational riders trying racing for the first time. I did okay but the racers who beat me in sanctioned races beat me in the senior games. There are time trials and road races. The senior games are less intimidating than a sanctioned race but the competition is excellent. If you race a time trial, it does not matter what other racers do. In your first race, you are guaranteed a personal best.
I cannot help with training. The bike will make very little difference since the routes for the games are typically on flatter terrain although they can be technical. If you race the time trial, aerobars would help. If you are not a very good bike handler with group riding skills then enter the time trial.
The only way to know whether you will enjoy racing is to enter and try it. There is no way to predict performance based upon age, weight, average speed, medical history and miles per year.
Insanity: doing the same thing over and over again and expecting different results. Albert Einstein