They are not the same, one says that you have been playing the guitar for 25 years and other says that you haven not played the guitar in 25 years. "I have been playing guitar for 25 years" = "Hace 25 años que toco la guitarra" it is a positive statement that you have played the guitar for 25 years. "I haven't played guitar for 25 years"? = "Hace 25 años que no toco la guitarra" It means that you haven't played the guitar for 25 years.. The first is positive the second is negative.