Kenneth Lonergan talks about his critically acclaimed play “This Is Our Youth,” set in New York in 1982. He’s joined by Kieran Culkin, who stars in it. The play follows 48 hours in the lives of three very lost young souls: a dejected 19-year-old who has just stolen $15,000 from his abusive father; Dennis, Warren’s charismatic drug-dealing friend who-helps Warren put the stolen money to good use; and Jessica, the young woman Warren yearns for. The play also stars Michael Cera and Tavi Gevinson