Stipulations:
- You cannot die and are immune to disease
- You cannot alter the future such that you change the world from your point of origin. i.e. You cannot become so famous that future people recognize you as immortal.
- If you vary the timeline too much you will cease to exist.
There is the caveats they put in that you’ve got to make sure no one finds out how immortal or you’ll just cease to exist and can’t change history in any significant way or be met with the same fate