Dietary changes at 40

Despite the fact that I admit to eating pizza and other unhealthy foods, I consumed some fruit today. I feel great at 40, but I realize that I have to eat even better.  It is hard to cut out the processed foods because it seems like most foods are processed.  My question is is there a link between age, PCOS, and other factors?  I am just concerned about my health and I do have a tendency to procrastinate.  I would like to change that, too.  I have been told that I need to adjust my diet because it will be harder to lose weight at my age now than I did in my teens, 20s, and 30s.