I played in a campaign which lasted for 4 years(in real life)and a 100 years(in game time) and we went through several characters from level 1 to level 15 ,unfortunately some of us graduated so the campaign had to end..
i dmed a near epic game level 17-21 and I didn't have many problems,maybe bacause my players were optimizers......
I think that is possible to play in epic level as long as there is an understanding between the players and the dm....