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There are several reasons that you can had flickering lights or photopsias in both eye.
Assuming that you have no other medical or retinal problems you could have a posterior vitreous detachment- This is when the gel material inside f your eyes start to liquefy and pull away from the retina. This is a normal degenerative change that occurs during the ages of 60-70. I see that you are 91 years old so this may have already occurred with you. You may just be experiencing floater which may appear as flickering lights. If you are also experiencing headaches, you may be having what we call an "aura".
Worst case scenario- you may be having a retinal tear but it is very unlikely to have a tear concurrently in both eyes without have had an inciting factor such as an infection or trauma.
If it continues for for more that a few days, I recommend seeing your ophthalmologist.