Here, "takeaway" means "the thing you should remember after you finish reading or listening to me."
"I have told you a lot about my mother, but I want you to remember three takeaways when you meet her: always compliment her cooking, never mention politics, and give her something green as a present. If you remember those three things, you can forget everything else I've said."
In your example, the author is saying:
You can learn two main lessons from everything I said. One is X [whatever he said in the last sentence], and the other is that I am becoming old, and might die soon.