The concept of "straw-purchasing" is commonly misunderstood. Legally, it is a "straw purchase" if you buy a firearm to give or otherwise transfer to someone who is legally prohibited from owning a firearm. Purchasing a firearm to give or sell to another person isn't in and of itself a straw purchase. Otherwise, you couldn't buy a firearm as a gift for someone. Furthermore, federal law prohibits people less than 21 years of age from buying handguns from a licensed dealer but it does not prohibit them from owning handguns, purchasing them privately, or receiving them as gifts. If you buy a handgun (for example) as a gift for another person who is legally permitted to own a handgun, you are not lying when you answer that you are the actual buyer of the firearm. It's then perfectly legal to give or sell that firearm to that person.
That said, if you purchase a handgun for the express purpose of transferring it to another person, you'd better be darned sure that person is legally allowed to own it. Even if the transfer doesn't violate federal law, a good prosecutor might be able to make a "straw purchase" case if it appeared to skirt state laws. Additionally, a resident of one state can't legally transfer a handgun to a resident of another state without going through a licensed dealer. Does it happen in face-to-face transactions? Sure, all the time. But it's illegal and if you get caught, the penalties are severe.
Edited to add: I am a federally-licensed firearm dealer. I'm not just pulling this information out of my backside. My advice to you is to steer clear of the deal you describe. At the very least, it skirts the California law which (as I understand it) requires all handgun transfers to a California resident to go through a licensed dealer.