Assume that the future can change based on your actions, so any historical information that you bring along with you from the intervening 25 years may quickly drift out of the new realities history.
Edit: also assume that you can be given a healthy 21-year-old body if you want or take your previous self’s place.
Further, identification will be provided for you if you were not born at that time.
I think as long as you’re careful you could avoid crashing the market until you are ready, and they would have to prove insider trading. I could spread my stock purchases through a bunch of shell corporations as well