sam: I know the twink look is appealing to many guys, and it seems -- especially if you're saying you'd ideally like to have *less* muscle on your frame -- that's what you're going for.
If you are hell-bent on losing more fat without gaining muscle, just eat less food. Try to eat a little something when you feel hungry so your body doesn't go into starvation mode, but cut your overall calories. Do short periods of intense aerobic exercise to help get your metabolism up. Don't increase your protein consumption and you won't put on muscle.
That said, body fat percentage is only one of two important numbers here; the other is LBMI, the lean body mass index.
Your LBMI is calculated as your lean body mass in kilograms divided by your height in meters, squared.
Your lean body mass is just your weight minus the fat, so if your body fat percentage is 10% or so, your lean mass is 90% of your weight.
lean mass (kg) / (height (m)^2)
In your case, you say you're 150lbs and 5'9". I'm a little surprised you'd weigh 150lbs, since you look like skin and bones, but assuming that's correct, let's say your body fat percentage is 10% or so, then you'd have a lean mass of 135lbs (150 * 90%) and you plug that all in and you get a LBMI of 19.9.
Here's a chart of what LBMI numbers essentially map to:http://www.csupomona.edu/~jvgrizzell/fitnessassessments/lbmichart.pdf
19.9 is approaching "triathlete," and you don't look like a triathlete. I'm skeptical of your numbers (specifically, I don't believe you weigh 150lbs) unless you have abnormally high bone density or massive, Lance-Armstrong-like legs that you can't see in your photos.
Understand that the lower your LBMI is, the harder it will be to keep fat off. Many twinky boys I've seen have the fat you're talking about, and because they're so concerned with not putting on muscle, they don't eat much protein, they certainly don't lift weights, and as a result their bodies preferentially eat up the muscle tissue for energy instead of the fat.
Josh Hillis, who has a great fitness blog, refers to this phenomenon as the "skinny fat" look -- when a person looks very thin, but at the same time doesn't look healthy. Too little muscle mass.http://joshsgarage.typepad.com/articles/2007/02/skinny_fat.html
Look, your body likes to keep some fat around. It's easy (relatively speaking) to lose fat down to a homeostasis of around 15% body fat or so, for most people ( 3% for genes), but getting lower than that takes a change of approach.
One possible change of approach is to keep your lean mass up, your protein consumption up, and your calorie intake down, allowing your body to maintain the muscle tissue that uses up the energy that coaxes the body into letting go of those fat reserves.
If you won't take that approach, frankly, the other option comes down to starvation. Your resting metabolic rate won't be very high without muscle tissue on your frame, and the less you eat, the more your body will reduce your RMR because it thinks you're on a desert island starving to death. That makes every pound of fat harder and harder to lose, it means your body will lose muscle tissue along the way, and you'll probably end up with relatively low energy levels and possibly health problems.
I think the only way to look like a twink and be healthy is if you happen to have an insanely high metabolism. Some people do, it's just how they were born, and have to really struggle to keep muscle mass on, and that's fine.
But since you're asking about how to lose fat, that is apparently not your situation. So yeah, you can lose that fat, but maybe consider reevaluating your ideas of what's sexy, first. No reason to end up hospitalized from starvation and an eating disorder at age 18!