Ok, so your small...
Im even smaller than you by 15lbs, so i know your problem. You dont have the downhill weight (obvious problem 1) and secondly, you dont have downhill power. (because you are small) Now Im assuming you can break and corner correctly and thats not an issue here.

You are going to have to learn to tuck in on the bigger guys. This is not as easy as it seems. The reasons people have gaps on downhills is because of breaking thresholds. Even pros on downhills have gaps between riders. This is because you are on a few seconds delay when someone in front of you goes into a corner, so there is a "domino" or "sling shot" effect. (Same thing as when someone accelerates out of a corner first, you have to accelerate harder because you had a delay) So you have to learn to modulate your breaks REALLY well if you have to keep really close to somebody in front of you. This is a skill that every small rider has to learn if you are going to race or descend with bigger guys. Its very easy to lock your brakes because if the person in front of you tightens their brakes, the effect is amplified to you because you are delayed a few seconds, so you are break harder than them... if this makes sense.

Secondly you are going to have to learn to pedal, and I mean REALLY pedal. Im not talking the nonsense you do now on downhills. You cannot "glide" down as the big guys do... when you tuck down to your handlebars. This doesn't work for small riders. If you do this, all you are doing is slowing down. Your weight compared to wind resistance overpowers the effort. You have to pedal almost the whole way. Dont use a heavy gear (53-11 or 53-12), again, you are just going to slow down, you dont have the power. The wind is stronger than you being so small. Use a 53-14 or so. And pedal. Im talking around 130rpm. Tuck as low as you can into your handlebars and spin so fast you're legs are just a blur. Now believe me, this sounds simple, but its not. Third, you have to accelerate like youve never done before out of corners. You have to stand, criterium style and GO! Then sit down and keep pedaling. As a climber, I have always pedaled almost harder coming off mountain passes than going up them. Believe me, your heart rate should be just as high if not higher when going down.
Learn to do these two thing and you will descend faster than you buddies, but its dangerous, and you have to have cadence. (as a small rider you should be training on cadence anyway, power meters and heart rate monitors are useless for small people, I have have always trained on cadence only)

As for wheels thus, get the lightest possible wheels. Your strength is climbing. Make sure you outfit yourself with EVERY SINGLE POSSIBLE ADVANTAGE for going up, and going up fast. There should be no stone left unturned for when it comes to going uphill fast. Choose the lightest handlebars, lightest waterbottle cages, EVERYTHING.
Choose wheels with good bearings and axles. Shimano make THE BEST axles and bearings combination. Other wheel makers make good wheels too. The reason I mention bearing and axles is that as a climber 70-80 percent of the time you are out of the saddle. Your twisting the front wheel all over the place and straining the back wheel. I used to go through so many bearings. Choose the lightest wheels you can afford. Ceramic bearings can be added if they dont come with the wheel.
I am still personally deciding between deep dish or shallow rim. Since you are small, flats are cumbersome, and you could use a fast wheel, but then again, just ride behind the big boys on the flats, and when the hills come, bring on the wrath and voyage into the distance alone. I use the shallowest, lightest wheel I can afford. When I get limpets on climbs a simple few strokes on the pedals cracks them due to the rapid accelerations of having light wheels. Never summit with anybody, and be clear on this.

If you ride campy, Fulcrum is a good option since its made by campy. They have a good light option or two. Mavic makes some really good wheels. Easton and Ritchey to me are good, they all are most probably made in the same damn factory in Taiwan anyway. Shimano is among the top wheels, HED is useless, even though they made really light wheels, Zipps are good, but are on the heavy side. But there are many great options these days. Dont worry about weight limits, thats a good advantage you have, you are not going to be breaking any wheels, trust me. Just avoid HED wheels, even small guys break those.

Hope this helps.