"Yes, we accumulate wisdom, but what use it it to us? Because the even's when the wisdom would've been useful, they're over and gone."
This is Tony's conviction about life. He reserves no value for experience. Now that he is forty, this worldview is costing him because he cannot bring himself to recognize any value in how he's lived his life if not to gain experience.
"If only I could go back in time! If only I could start my life again knowing what I know now."
In perhaps the most directly indulgent line of the entire play, Tony gives voice to the dilemma of adulthood. Having gained so much knowledge, Tony now wishes he could communicate with his younger self. Now he has the knowledge, but he doesn't have the opportunities of his younger self. He feels trapped too far down an unrecoverable path, but now he knows enough to recognize that he's trapped.
"We're actors."
This is Tony's ex's explanation for flippancy. She doesn't take herself seriously because she treats life like a production. She's merely playing a role. In a sense, she's asking him not to take her too seriously either, but at the tail end of a relationship this is not a very welcome or even appropriate refrain.
"An actor is repeating a part, but this is different."
On Crimp's part this line is delightfully ironic because the character of Tony is literally being portrayed by an actor in a play. For the character, however, this line is delivered with sincere remorse. Tony recognizes that the stakes are serious for his life. His girlfriend's flippant approach is not sufficient because Tony knows there can be no second takes.
