Normally, every 7 years that passes, every cells in a human body are renovated. Do we change your thoughts because of the cells, which are renovating, or because of the influences and thoughts from the society which we live?
Peter Naur (Turing Award) has the following theory of mental life in terms of neural activity (synapse state theory of mental life). You might want to take a look at it:
http://www.naur.com/synapse-state.pdf
From a small conversation I had with him, I got the idea that for a new thought and habit to be formed you have something like a new connection between different neural elements so far unrelated, where each element maps a concept. So the novelty might come from the new connection. Probably exposure to the societie's environment plays an important role in growing and activating such connections.
One curious thing about this theory (more in terms of habits than thoughts) is what seems to be the plasticity of the connections. It seems that if you change a bit, you get a sort of "permanent deformation", that tends to hold at least partly if you keep insisting. If it is true, I find this a very interesting natural asset against common drawbacks in habit change.
These are just very rough ideas I got from Peter (and probably distorted them a bit). Even if they are correct, I can not justify them since this is not my area at all.
About the possibility that thoughts change because of cell renovation I remembered something funny. Though I am not an expert, I doubt it works just like that. If it did, every marriage would probably last at least 7 years.
I do not think we will change our thoughts every fixed number of years as thoughts are activities of our mind that deals with what we have in our memories as collective and cumulative set of facts called knowledge. Thoughts are not erasable and replaceable but instead can be augmented, sharpened and strengthened for better understanding of things.
Established cultures, proven theories of science, every truth of things we do daily based on our thought processes will never be changed as our cells do. In fact it is not even necessary and in fact more destructive and wasteful, for if every time our thoughts change we need to create or established results anew, tantamount of re-doing what we have done and established to be true.
The "Observer Effect" is one of the new understandings in Quantum Science. Quoting Dr. Wayne Dyer, "When you change the way that you look at things, the things you look at, change."
From Bruce Lipton we know that environment modifies genetic expression.
Therefore I would suggest that thoughts are not a product of biology, rather the reverse is true.
Our thoughts reflect much more social surrounding than biological. We form our thoughts based on responses from the society. For example, I know the consequences of killing a person: I face retribution by the law and I don't want to end up in such scenario.
To change our thought we have to want that and perhaps we believe they are hurting us in a certain way that must be changed.
Changing attitudes requires motivation for such.
Out of curiosity, a musician and composer sec sixteenth and mid-seventeenth, Claudio Moteverdi had much success in operas (Orpheus, etc) and their madrigals, because his background in psychology allowed him to apply their knowledge about emotions and attitudes in his music. He took the most of his time. He wore very virtuous artists because they had not only to know music as they had to represent the dramas in a committed way ....
... or ... Who dominates human psychology is one step closer to getting what they want ... as satisfies people .... at least occasionally ....