I am doing something somewhat similar. I had to lose weight so I started with that. Just by changing what I eat, I’ve lost about 22 kg in about 4 months. Once that was done I started exercising : football, badminton, squash, treadmill, cardio. Once I did this I found that I have to eat. The more you exercise, the more you have to eat, for your body to recover, muscle to repair itself. I am over 40 as well and I know damn well it’s not easy.
It’s just the 1300 calories per day feels insufficient if you exercise seriously as well.