What makes you think "I'm too young for this"?

Earlier today I realized how “old and crotchety” I’m getting. I’m only 26! But with the way my temper/attitude/state of mind has been lately, I think I ought to just get the transition over with and ask for a rocking chair and a garden hose for Christmas so I can sit out on the front porch and chase kids off my damn lawn.

What habits/attitudes do you display that make you seem/feel older than you really are?