I have decades old wool sweaters. And my oldest wool base layers must be 10 years old. It's not a problem. If you dig it down in the ground or dump it in a lake it will break down with time.
Wooly jumpers, especially when made of fragile merino wool, remain usable for much longer when they are made of a mix that includes plastic fibers (maybe 75% merino, 25% polyester).
The sweaters are 100% wool, but are the thick knitted type. Think a classic fisherman sweater or the Icelandic lopapeysa. These are not merino. Base layer is merino, might be a polyester/wool mix.
