Is 38 too young for a midlife crisis?

I have been restless and dissatisfied for going on a couple years now, but no major events (that I can identify) are the cause. I’m constantly daydreaming of ending my 16-year marriage for a variety of reasons, but nothing new— all issues that have been around for 5+ years now. I’m afraid to even bring it up with my wife or any close friends because what if this is some kind of “midlife crisis” that will pass?

Anyone else feel a need to change things up in their late 30s, despite having what many would consider a pretty contempt life?

*EDIT— you guys are awesome! Thanks for sharing your stories and thanks for the book recs. Also, I do have a basic understanding of math and life expectancy. I don’t believe the term “midlife” is meant to be literal.