I feel my age.I can not remember why I came downstairs.I have put the remote in the fridge when getting something to drink.I am not sure, but it may happen to be the best of us.　 この表現は自然ですか？

You can say "I feel my age" but it doesn't sound super natural.

I feel my age. I cannot remember why I came downstairs. In the past, I have put the remote in the fridge when getting something to drink. I'm not sure why, but it seems to happen to the best of us.

-I included "in the past" because the first sentence is in the past tense (as if it just happened) and the second sentence is in the past perfect.
-And I changed up the last sentence to make a little more sense.
-You could maybe say something like: "I can really feel the affects of age" -just an idea, hope this helps!