cusp a point of transition between two different states: those on the cusp of adulthood.
There are other meanings, of course, but this is the one that applies to me right now : I am on the cusp of very very old old age, because of my brand new GREAT grandchild. I must have mentioned Elise Boulding to you before now.
Elise Boulding (1920-2010) was a sociologist who coined the phrase, "the 200-year present", that gives us a perspective of time - past and present - within one's personal reach and understanding. Consiider the ages of the oldest and youngest persons you know and there you have within your lifetime a span of about 200 years to draw from, past effects and present conditions, from which you can extrapolate some personal predictions of the future. That's very exciting. I'm part of my new little girl's past and of her future knowledge.
More to come. I'll make a list so I won't forget.