Hopefully my input here is of some help. I will be 37 this August, so not that far removed from you agewise. I had trained for about four or five years, and then had several events happen in my personal life almost all at once - a new job, a new baby, several illnesses in the family, a death in the family, my wife losing her job due to sed illness . . . long story short, I ended up taking an unintentional hiatus . . . which ended up lasting three years.
I am also out of shape, and have put on some poundage as well. I started getting aggravated at things far more than I should be, felt tightening in my chest when I was stressed, and just all around felt something was out of balance in my life.
One week ago yesterday, I headed back to the dojo for the first time in three years. My Sensei was very excited to see me back on the mat. I practiced for almost four hours that day - in fact I think I overdid it, because there was one point I was barely able to breathe. But when I trained Wednesday, my breathing was better, and things started to fall back into place. Same thing when I hit the mat yesterday.
After only a week back, I can already start to feel the benefits; I feel calmer, more focused; some of my irritation at pointless things has gone away. The pressure in my chest has stopped. And I am more engaged in trying to apply the principles of Budo to my own life.
Some of my techniques are still rough, sure. Things need to be worked on. But that's always the case, isn't it?
My advice to you: Hit the mat as soon as possible. But take it slow, but consistantly. Set a mionimum for how many times you will go to class that week . . . you can always ramp it up later and go to more classes if you are able. If you are worried about what you can and can't do at this point, talk with your Sensei about your concerns: No good Sensei will put you at risk of needless injury. When you do your techniques, go slow at first until you have the movements down fluidly; speed will come in time.
After your first few classes, your muscles will start to re-adjust. You'll be hurting, you'll be achey (Aiki?
), but you'll be glad you're back.