My CTBs are 15 years old. Liners still look good. My left boot does have a dime-sized hole worn through the lining layer in the heel area. But, I never noticed it until I just did a visual inspection before responding to this post.
FS: 2009 BMW R1200GS
, '05 GSX-R1000
Iron Butt # 4999, (former) WERA/CCS EX # 666, AMA Life Member, Drummer, Bassist