I have a 1993 and the belts were never changed and as the second owner of the bike and the age the belts were changed, interesting things one was beginning to delaminate (come apart). Just like the post above says it best. Better to be safe than sorry.
I just had the belts changed on my 1997 GL1500 with 40,000. I figured they were 13 yrs old so I better change them. However, the belts they took off looked really good. Even the seals looked good.
No cracks or fraying at all.