Over the weekend, I had my body analysis done by a MD at a local hospital. They hooked me up to a machine, kinda looked like an EKG machine and it measured my body fat, lean mass and average calorie burn. The results are a little puzzling for me. They are as follows:

My bodyfat is 20%. Someone my age should be 18-25%. So I'm okay there.
Lean mass is 132 pounds.
I weigh 167 pounds. (i weighed 160 pounds 3 weeks ago before I started my running program and weight training. I didn't gain inches but I did gain 7 pounds of lean muscle in that time....I guess. My clothes fit better and I feel great. Despite the weight gain.)
I burn 1791 calories a day just by breathing, and
My ideal weight should be 162

Now My goal weight is 140, but I now don't think that is achievable if I have 132 pounds of lean mass. My body fat is right on target and I'm very healthy according to my bloodwork i had done on Friday.

So my question is, can I change my body type with exercise? I would like to weigh about 150 and reshape my hips and thighs and develop 6 pack abs. Can I achieve these things and be at a healthy bodyfat percentage? I know if my fat is too low, it can cause some health problems.

I'm trying to set realistic goals, but I always plateau at 159 pounds. I can't seem to diet pass that point. I've been in the 160 range for 6 months now. Is being 160 my destiny? Please help.

Thanks.