There is no such thing as might just be my age. As a personal judgement it is the route to a care home - and if anyone says that to you, especially a GP. Get them out of your life immediately.
Life is for living at any age and in any state of health, never just passively accept anything, push the boundaries.
A number of people have suggested possible causes: aneamia, Type 2 diabetes. I will suggest another - Sleep apnea. This is always connected with men and heavy snoring, but DH has just been diagnosed with it - and at the severe end, yet he rarely snores. I had been telling him for years that if I woke in the night, I would sometimes count to 30 between his breathes, but he wouldn't believe me. However he recently began having long 'rests' after breakfast as well as after lunch and in the evening and agreed to see a doctor. After using a home sleep monitor, for one night, he got the shock of his life to find that not only did he suffer from it, he was down the severe end.
So do not discount it, because you are unaware of it having this problem and rarely snore. Most people with it never know and therefore receve no treatment.
I am 76 in - OMG - under a fortnight, today I was up at 6.00 am as usual, went for a long walk at 6,30, spent 4 plus hours in the garden, spent an hour processing the crop from the kitchen garden, did the week's shopping, SM and local town centre and spent over an hour cleaning. I will probably be in bed by 11.00. My back aches a bit, but otherwise I still feel bright and active.