Well first you realy don't have to be skinny. For exsample, most bases are pretty big and strong. Of corse you can't be fat but you don't have to be skinny.
Second streach every day. Start of with easy things like touching your feet without bending you legs,speard your legs out and touch each toe twenty times,go as far into the splits as you can.After about a week of doing that every day you'll be able to put your palms to the ground without bending your legs,you'll be able to put your nose to each of your knees and you'll be able to do the splits.It's all a matter of time.