The Yankees drafted Jeter out of high school in 1992, and he debuted in the major leagues at age 21 in 1995. The following year, he became the Yankees' starting shortstop, won the Rookie of the Year Award, and helped the team win the 1996 World Series.
What you want is an open return ticket. The outgoing flight is confirmed and the return is open. Depending on the type of ticket, the return can be up to a year after departure. You can book the return ticket after departure--subject to availability of course.
If you purchase the second seat at the time of original purchase, the second seat will be sold at the same rate. At a later date (or at the airport), the lowest ticket price available will be sold. If all legs of the flight have at least one empty seat, the second seat cost may be refunded post-travel.