The new Back To The Future video game is set right after the third film. But this game also shows the first time Doc met Marty... when Doc was a mere 17-year-old. Check it out.
In this first video from IGN the plot is mapped out for the Back To The Future video game. Marty goest back in time to get help from a teenage Doc Brown. Great Scott! Get the whole scoop from this collection of behind-the-scenes videos (including the voice of an uncannily good Marty McFly impersonator):