I am not sure what constitutes "starting" anyway.
Some zamboni's in congress have already introduced impeachment bills and I expect other losers will do the same just to score points with the folks back home. But those bills just sit there, and have not been referred to or out of committee and so on. But arguably introducing a bill is "starting" in which case it has already started.
I dont care one way or the other. It's all a kabuki dance with the outcome already known.
But to me, impeachment does not start until the Speaker of the House refers a members bill/motion to impeach to committee AND the committee votes - after hearing- to refer it to the full House. Anything less than that is just dicking around. There could be other definitions too, such as impeachment does not begin until there is an actual impeachment, ie indictment in the house. Either way, the point being that I think it should be more than just some impeachment bill being introduced. We have some of those already and will have more.