I'm pretty skinny and I'm 55. BMI is 20, body fat about 9%. For a lot of men, in terms of losing weight, fat around the waist is the last to go.

BMI is a function of weight and height, so musculature will affect it as muscle weighs more than adipose tissue. For that reason, I don't think anyone can tell you what BMI will correspond to fat loss.

If you want to lose weight, increase exercise intensity and eat reasonably.