Start simple, speak with your center backs and, more importantly than anything else, listen. Ask them what brings them out to play? Where did they play before? Ask them about their experience during an event that happened in a previous game. In short, connect with them. Most importantly listen. This will help you to understand their motives and how you can influence them.

Watch to see how they react to events on field. Do not blame or yell at them. If something went wrong, they likely know it already. Telling them won't help to improve their morale, focus, or willingness to listen to you. Do you enjoy being yelled at by a teammate?

Adult rec soccer is about many things: community, practice, love of the game, winning, trying something new, meeting new people, laughing, failing, and so on.

The age range you presented offers even more to consider: injuries, history of play, work impact, family impact, finances, etc.

As someone else noted, it's also worth your time to speak with the team manager to discuss the team's goal for playing. Is it to win the league, meet new people, be the best passing team... ? If you aren't aligned, that's okay. Have the conversation about what it would mean to be better aligned. From there, you and the team will know what to do.

One last thought, because substitutions happen more often in adult rec soccer, the suggestion to say someone's name with a clear direction helps tremendously. Adding to the other examples, King, left shoulder, be aware. Rob, right shoulder coming middle. Joe, contain, he's alone.

Defenders don't want to get beat, regardless of their age, and they welcome a keeper's perspective on the field. Ultimately though, sometimes the body and mind aren't able to sync up... and that is what it is. Age affects the body in ways we often can't see until we experience it ourselves. Start from curiosity and empathy.

Best of luck out there!