//OT
don't use impulse, its evil, use steam instead....
i have both, at least steam is functional every time and have some games to sell ;)
//end OT

Use the one that best suits your needs. I have zero use for any of Steam's 'features', so Impulse is the one I prefer. Others find it's the opposite.

Is there any specific reason why it would not be feasible for a parent or guardian to buy the game(s) for you?

but ain't that his money?

My parents bitched when I spent money on games but it was mine and they couldn't do a damn thing about it. As long as you get money legally, spend how you like.

An awful lot of parent aged people are lower tech and suspicious of security on the internet. Hell it took me years to persuade my mum to buy things over the net because she'd seen those "OMG C0MPUT3RZ STEALIN J00 $$$!!!" stories on current affairs shows

It's really quite ironic, seeing as transactions over the internet which are set up correctly are actually more secure than many physical transactions, such as handing a waiter your credit card to pay the bill at a restaurant.

Forget about money. I've had people refuse to tell me and/or confirm their name, yet they expect me to 'change the password' for their computer account and tell the what it is over the phone.
I think a lot of people get scared on security and go into tin-foil-hat mode on areas they are not that informed in.