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Without reading the terms of the lease itself, it is hard to give a definitive response. However, based on what you are saying, it appears that as of 2008, if you did not exercise a renewal option, you were on a month to month basis. As far as the late fees, this definitely seems odd. The lease may contain a clause that says that his failure to impose a late fee does not waive his right to do so in the future; but that is different than trying to go back 7 years to collect old late fees that he never timely imposed.
One common defense used against these tactics is that of "laches". Law.com defines that term as follows: "the legal doctrine that a legal right or claim will not be enforced or allowed if a long delay in asserting the right or claim has prejudiced the adverse party (hurt the opponent) as a sort of "legal ambush." Another defense is "waiver": "the intentional and voluntary giving up of something, such as a right, either by an express statement or by conduct (such as not enforcing a right)."
So, you should be able to defend against his actions on these two grounds.