In the fast lane
Definition 1 of 2
Pro Tip 1/3Not Literal
It's a metaphor meaning active and risky, not a physical road. 
Joining the startup, he felt he was finally in the fast lane.
Pro Tip 2/3Luxurious Lifestyles
Implies a lavish and possibly unsustainable lifestyle. 
Celebrities often get caught up in the fast lane.
Pro Tip 3/3Caution
Can have a negative connotation referring to recklessness. 
He warned his son about the dangers of living life in the fast lane.