AWST reports that Sen. John Glenn (D.-Ohio), the first American to orbit the Earth (in 1961), has a "..burning desire to go back to space..." NASA Administrator Daniel Goldin is reported to be considering his request to fly again. Glenn is 76 years old, and he would become the oldest person to visit space.
It is very unlikely that there will be any health problems due to his age, provided that he's in normal health - since going to orbit and living in zero G is not stressful. However, NASA is not allowed to carry people other than professional staff related to the work of each mission on board the space shuttle, and it seems unlikely that US taxpayers will wish to pay for his trip. Now if some company was only offering tourist flights... -SFJ