Sign of Aging?

When my mum was 50s, she told me she feel old. She said the same thing when she was 60s and now she is in her 70s. I always thoughts, you should not say that you are old because once you think you are old, you are old. But we can't admit that when time past by, we really feel the difference we are not young anymore.

I am in Toronto for business. I had flew to the west for meeting several times before but the jet lag had never hit me so badly. I tried very hard to adjust the time, like not sleeping in the afternoon when I feel sleepily, I expose myself to the sun, I drank lots of water and eat less carb but no use. Even though I was awake but my mind goes blank in the afternoon. I find it so hard to concentrate and not able to really enjoy the people around me. In the past, meeting like this I was able to work through the day and night, check my mails and sometimes took conference calls.

I do not want to admit it but if this is not sign of aging, what is this then?