Mine are over 11 years old but on their last legs; I intended to replace them with Costco Interstates this year, but illness put the kibosh on our traveling, so I'll just wait, nurse them along, and switch them out next spring. They've bowed out a bit since I can remember, but not to any extreme. Just this summer one or two of them began demonstrating odd cell behavior, with a middle cell overflowing and the other two cells dropping; so I suspect the internal walls have broken down and even solar charging is beyond their tolerance anymore. If that worsens I may replace them prior to winter.
11 years is not the norm, but watching the water and letting solar keep them up during storage can help take wet cells to and beyond 7 or so years. I intend to get a battery tester to replace my 40 year-old, long-ago failed one, as it can help monitor acid chemistry. That may provide info that'll help me decide whether to switch out the batteries before winter. My only reason to wait otherwise is purely to max the ultimate age of the new ones.
Joel