I let myself go a little bit between 39 and 43. Worked for a startup that was very demanding and stressful since it was bleeding cash after year 1. Often business dinners with cocktails and wine doesn’t bode well for early morning runs. 
Combine that with 2 kids in club sports and your weekends are pretty shot too.
I went to a new company, quit drinking except occasional glass of wine socially and now get in 40-45mpw. Push-ups 3-4 times per week. I run evenings now since my kids are teens and usually doing their own thing anyway. I look better, but more importantly I feel way better.
It is tougher getting out the door and running that first mile at 47 than it was at 31, but it’s manageable. Massage every 3 weeks helps too.