Aldo stopped kicking due to injuries, not due to tank. Aldo never had a great tank, and didn't diet properly leading to terrible cuts at times, but his cardio failed him during the Hominick fight due to a terrible infection that required antibiotics to the point that he had to leave the champions gathering early. Between the injuries, wars and hard training at NU, he was out of his prime.
As for the twelve year thing, it isn't definitive and everyone is different. There are guys who excel at a later age, or fighters like Holloway who start kickboxing at 15, got to the UFC at 21, and probably didn't hit his prime until he was 24. But it seems fighters tend to fall off to some degree around this time frame in numerous ways. People will say that Max is in his prime currently, I don't think he is at all. I do however think his fight knowledge, ability to implement his skill set and diversify his approach with it, as well as gameplanning is at it's peak. I don't think Pantoja is at his physical peak, but he's such a wily veteran that he can utilize his skills better than ever and knows his limitations. There's no cut and cry answer as there are so many fighters, but I feel comfortable in my conclusion with the realization that people are different and fight mileage, age and injuries alter fighters differently and they exit their prime with effects demonstrating themselves in innumerable ways.