I really enjoyed this movie, I watched it streaming on Amazon Prime.
The theme is time travel and the physics they discuss is pretty close to authentic physics. They mention CERN and the Large Hadron Collider, and not surprisingly used a theoretical physicist, a professor, as a consultant.
Younger James (actor was about 45) is consumed with developing his theories and eventual method of time travel when this older guy (actor was 61) shows up claiming to be him at an older age. He has a unique way of proving it, comparing unique markings on their Johnsons. In other movies it might have come across as too juvenile but here it worked.
So James and this new guy, "uncle Jimmy", go back and forth and create some unusual and mostly humorous situations. And of course there is a girl involved, and James must get his priorities straight. That is why his older self is there, to convince him.
Fun, entertaining movie.