Notable: We're how old?

Three new books help you gauge how much of your life now qualifies as history.

The Book of Cool (Running Press) by Marianne Taylor traces the history of that ineffable, desirable state, using everything from timelines of sunglasses styles to the top five signs a fad is done for ("A YouTube video surfaces of said item in blender.").

I Love It When You Talk Retro (St. Martin's) by Ralph Keyes explains the origins of colorful phrases for which younger people may have no cultural context, like saying someone sounds like a broken record or an object is bigger than a breadbox.

Obsolete: An Encyclopedia of Once-Common Things Passing Us By (Abrams Image) by Anna Jane Grossman, illustrated by James Gulliver Hancock, rounds up such vanishing phenomena as airport goodbyes, cursive writing and social e-mail.

Colette Bancroft, Times book editor