Is it a pluto issue? Perhaps maybe it’s nns squaring? I have found 8-10 years a real bone of contention in relationships too. I personally need to share pluto for it to be a thing before any serious thought is put into it.
It's not so much a Pluto thing; it's more of a generational thing (which, agreed, doesn't narrow out Pluto), but within social context. Generations have different social reference points that each relates to. For example, I was 22 yrs old when the World Trade Center attack occurred. For me to bring that up on to someone 10 yrs younger, who was 12 yrs old, they might really be able to relate to the intense memories I feel from it; it can create awkward moments and even leave the older person feeling alienated and misunderstood in the relationship, which is supposed to be their source of emotional fulfillment. Multiply that formula over for music, fashion, celebrities, and one person's bound to question the relationship's appeal;
There's also the physical appeal; even someone who'se normally very confident might feel the need to go to extra measures to appear more fit and even youthful, out of fear of loosing their younger partner at any point. It could create a complex for the older person, while the younger person could pick up on vibes of insecurity and loose respect for their older partner.
Then there's life stages; in her 50's, Lisa Bonet for example was much more complacent to stay home and work on herself, where Jason, in his forties, still had a lot of partying to do. Jason would often send pictures of himself to her from wherever he was, having a good time. (Really sounds more parental). Every new decade makes a person have to re-evaluate what's important, based off slowing down to balancing physical health, mental health and spiritual health. Even if we're young at heart, the body breaks down. We're kinda forced to re-evaluate our life style and become more tempered and complacent with smaller things.