AGM batteries will probably last at least twice as long as liquid acid batteries if one forgets to keep the liquid levels high enough in their liquid acid batteries, or if one remembers but postpones keeping the liquid levels high enough because their liquid acid batteries are a pain to access.
Our first set of AGM RV coach batteries lasted around 8 years before I replaced them just-in-case (they were still functioning when replaced). They were taken care of by only the stock 13.6 volt fixed voltage RV converter when parked, and the RV engine's alternator when traveling.
The AGM starting battery in our occasionally used pickup truck just sits there under the hood ready to do it's starting job with no attention from me between uses - but I do dust if off about once a year.