Can you go to Wal-Greens to buy condoms at a young age without a parent?

I want to buy a condom at a young age, really young, and I want to know if I can go to my local Walgreen's to buy it, but without my parent or a older sibling, just by myself. Will they need any ID's or any info, or a legal garden to be with me, or do I have to sign something? Also, how do you know you what size to get. What do you have to do to measure your penis to get the right size condom. I'm pretty sure you don't use a ruler, I think it's D.M.I or whatever that "South Park" episode was called. If want want to know how old I am, your not, just tell me what age do you have to be to get a condom without a parent in Las Vegas, Nevada.