I think you'll be fine. Lots of old dudes on group rides in various stages of fitness.
It's a pet peeve of mine that people have blinky lights in a group ride. Are you getting a police rollout for the first few kms? If a large group of cyclists and a police motorcycle unit don't make things 'visible' then a little blinking light isn't going to either. Once things thin out you can stop and flip the lights on, or do it from the bike computer if you have all ANT+ lights.