I've just turned 28 and I injured myself playing squash, I tried to live without the ACL for about a 2 years as I had to contend with the birth of my son so it was all a bit hectic.
Unfortunately having no ACL is no way to live for even a semi active person, I was unable to run, play catch with my nephews and do alot of the semi childish things we like to do on a daily basis without it giving way and had to completely forget about proper sports. Likewise mine fully snapped and left to its own devices rotted away, I had no initial surgery after the tear.
If your leg is stable and it doesn't cuase you any problems then I wouldn't worry too much, it certainly didn't effect my cycling. But if it stops you form doing other things you certainly have a case to have it repaired and it doesn't matter how long ago the injury happened as the graft is a complete replacement.