Senility Rocks!

Uttered after a memory lapse or a brief interruption to intelligence affectionately or laughingly attributed to age.

1) A: Where did I put my pen?

B: It's there in front of you!

A: Doh! Senility rocks!

2) A: Did I tell you I'm going out tomorrow?

B: You did - seven times now.

A: Oops - Senility Rocks