I was in the same boat for years. Its the trims. I was doing the same thing you did. I went to the salon every 3 months and she would cut off 1/2- 1 inch and I couldnt understand why it wasnt getting longer. If your hair is only growing 1/2 inch a month then on that third month you are only left with 1/2 inch growth after you get it trimmed and that would be if the stylist were precise which usually doesnt happen. So you end up always staying the same. That is happening to me now again when I thought I knew better. My new stylist knows I am growing my hair and I told her only dustings but the last two times I went she took more than I wanted each time and set me back a good bit. I just decided I have to stay away from the salon if I want any growth. They mean well but cant seem to take a very small amount. So from now on its self dusting for me. We'll see if the plan changes when I get to whatever is my goal but for growth its best to do self dustings for me anyway. I am also over 40 and shooting for waist.