I was 70 this year. In my younger days, I weighed around 8 stone (I'm short) and never had to think about what I ate. I had 4 children and was very active.
As I got older, especially post-menopause, I got less active and ate more cake/biscuits/chocolate.
Just before my 70th birthday, I finally checked the scales, to find I was more than 2.5 stones over "normal" weight - a real wake-up call; I was slowing down, finding it harder to walk any distance, and was aware that I would do anything to avoid bending down
.
I asked for a Fitbit for my birthday and started to do 10k steps a day. Initially, I cut out all chocolate, all cake, biscuits and most bread, though I now eat them very occasionally - the craving for chocolate has all but gone and I find sugary foods sickly now. I've always eaten well so I just watch my portions and refuse the puddings. I eat protein-rich meals and don't snack in between.
Within 6 months I had lost 2.5 stones and I feel so much better. My aches and pains have largely gone, I can walk for miles, and I have far more energy.
I strongly recommend not thinking of this as "going on a diet". Just get yourself healthy - eat less, eat the right stuff, cut out the rubbish. A bit of exercise will help, and it will also distract you from constant eating, but the main thing is to reduce your food and don't eat sugar.
Good luck!