Evolution works in exactly the same way, in terms of a buildup of changes.
If all your ancestors of the past 10 million years would hold hands and you'ld go back looking at their appearance one by one, there would be no single individual of which you would be able to say "this one is not a human", while the one right next to it is a human. It doesn't work that way, because evolution is a gradual process.
The same goes with your age indeed.
If you'ld look at a picture of your face from every day of your life, starting as a child and ending as an adult, there would be no single picture of which you would say "in this picture I'm not an adult", while in the picture right next to it you are an adult. It just doesn't work that way.
Here's a nice analogy using color:
View attachment 46802
Sorry if you can't read it, I didn't immediately find a better quality picture.
Anyhow, the text starts out as read and ends in blue. Please, show me the "first" blue word in the paragraph, where the one immediately before it, is still red.
Evolution is the exact same. It is the nature of gradual change.