Falling Out

In 1989 George and Neal had a falling out and didn't speak to each other for over 40 years, until they reconnected over their love of "Rock Smoothies". When they invented their time machine a few weeks after reconnecting, they decided that those 40 years were pretty foolish. So, they traveled back to 1989, killed their previous selves, and carried on as if nothing had happened. No one ever questioned why they aged 40 years overnight.