First you have to scope out the course and the competition. Senior Olympics / Games is a total crap shoot on who will show up and in what condition. Ideally, you want experienced riders so that it is not a crash fest which it can be. The older guys can be the worst. Sorry but it is a reality. I did a senior games event once and the range of ability was vast from USCF Cat 1/2 racers to absolute beginners who did not have a chance and were totally clueless.

As far as training, for a road race at 5 10 and 190, you are too heavy so the easiest thing to do to improve performance is to lose weight. You need to drop at least 10 pounds and more like 20. That will give you more advantage on the hills. As far as training goes, road races are decided on the hills. Determine what the course will be and start practicing climbing hills that are similar to what is on the course. The other thing to do is ride a lot in zone 3 which will be the zone in which you will be during the race. Work on your pack skills and get comfortable riding in a group at 22 to 25 mph. Do not assume that these guys are going to ride slow. I suspect they will go pretty fast. They may not go as fast as the USCF 55+ peloton but it may be close. Good luck.