My tank is now 3 years old and I'm noticing its become more prone to spots of GBA over time as detritus builds up in the soil. Some plants dont grow as fast as they used to, despite light and co2 staying the same, possibly due to depleted soil. I dont always add clay so after a few years its done. I usually use ADA or glassgarten soil. I also have to admit I'm a lazy maintainer, so I'm sure someone who is more diligent can probably stretch it a lot longer/indefinitely without issues, and even the soil being depleted could be resolved by using roottabs or something. But much like our interior and garden, we like to switch it up every now and again. Same goes for my tanks, its great to see something grow and mature, but after a while you want to see something new 🙂 I'm fine with having to redo every few years. No wait, that suggests its passive and I respond. But its not me responding, I actively want to redo my tank every few years.
My main issue with that is always, what do I do with the leftover fish from the old scape. This far, they've been staying with me, but you get a lot of small groups/lone survivors that way in the end.
But yeah, I do believe tanks have a break-in period (ranging from the first month till about half a year depending on skill of the maintainer/owner, then a golden period that extends from the moment its stable till... maintenance is dropped due to boredom or necessity, or something changes that disturbs the balance (lights go bust or something) or something like the soil gets depleted (but I think owner getting bored/too busy and dropping maintenance levels is a far greater cause of decline). Then there is the decline state, where people just let it run its course till rescape 🙂