For reference...I'll be 33 on Monday.
First felt old when I started losing my hair at 28. Knew it was downhill from there.
Earlier this week I played a one-on-one game of bball with a 14 year old and he destroyed me 21-5.
But you know what makes me REALLY feel old? When older relatives start passing away. Since 2007 I lost my aunt, grandmother, great grandmother, and three family friends. When family an friends who had a significant impact on how you developed in your formative years start passing away due to old age/complications, you really feel your age then.