1. It is not a time travel movie but time inversion. If you are inverted, you still age. You won't become Benjamin Button. If you go inside the turnstile to be inverted for one year at the age of 30, you will be 31 years old when you enter back the turnstile. Sator received the tech from the future people (unknown) where they sends him gold as payment for retrieving the Algorithm pieces. Whatever Sator decides in the current moment will change whatever outcome of the new future. The future people gave him instructions on how to make the turnstile by burying it in the inverted capsules (remember when the gold bars he received on the yacht was inverted?) so that he can make use of it.

2. To close all loose ends about the knowledge of time inversion

3. Shot by Priya? She called The Protagonist using the special phone given to her in case she feels her life was threatened. As for shot by Sator, she does not know in advance.

4. You can't live long in reverted entropy. You eventually need to step back into the turnstile to be back to normal. In this case, Young Kat went into the turnstile to be inverted, and uninverted back to be back at Old Kat. This was shown off camera.

5. Neil lives in a loop. Kinda.

Tenet FAQ