I don't think we should really put too much stock in Itachi's words that the Uchiha Clan piled up "many sacrifices" throughout its generations... we know now that the MS can only be awakened by sincere emotional trauma/suffering... simply sacrificing someone because you desire power isn't enough, you have to actually love that person, too. It takes extreme circumstances for that sort of mentality to arise, where one's desire for power overcomes their dearest bonds... Sasuke is the only Uchiha in the series so far to have tried to willingly kill someone for the MS, and even he couldn't go through with it. Every MS shown has been activated accidentally after a life-changing trauma.
During their fight, Itachi was trying to make Sasuke fear/hate him, and did so by lying about why he needed Sasuke and why he murdered the clan.
This may be a weaker point, but Tobirama's description of Uchiha awakening the MS when they come to lose "intense feelings of love" does not seem to imply any willingness to sacrifice such feelings... you'd think someone as informed on the Uchiha as Tobirama would have some idea that intentional sacrifices were occurring. You'd think Hashirama would have learned of this, too... after all, he and Madara entered into an alliance and were close friends. Why wouldn't Madara open up to Hashirama about the Uchiha clan's "curse" if it involved intentional sacrifices?
In my opinion, the "Curse" of the Uchiha clan is just as Tobirama described: an excess of Yin/mental energies that can run out of control and affect their reasoning if left unchecked after extreme circumstances. And the age of 7 isn't some magical clue, it's probably pure coincidence.