I think you should have enough evidence to be granted a six-month leave as visitor, but of course I cannot guarantee it.
What the UK Border Agency is worried about is a) illegal work and b) overstay. You are providing documentation for adequate savings and support/sponsorship from your aunt, with her pay slips and bank statement. And you have strong ties in US (having to return for your SATs and graduation), which make overstay unlikely. I suggest you dress neatly, be friendly and polite, and answer their questions truthfully and succinctly, without volunteering information not asked for. And only show your supporting documents when asked.

As for a stopover in Qatar, that shouldn't matter.

The one thing you don't mention is medical insurance.

The UKBA is also concerned about your being a charge on public funds.

I would have thought any border control official would be astounded meeting an American coming for five months without medical insurance, and assume the only possible explanation was that you were expecting to get free treatment here you can't get at home. It must be essential to demonstrate you've got cover and that it will be honoured here by your insurer

Agree that medical insurance might e a hitch. It sounds like you are probably covered under your parent's medical insurance. If so, be sure you have the appropriate card with you - as well as a letter stating that they will cover you or expenses outside the US. This should be fine as long as they don;t belong to an HMO that allows charges only from member MDs and facilities. If they do - you may need to purchase health insurance (perhaps as part of travel insurance) for the time you will be out of the country.

Of course, all of this depends on the OP declaring they intend to stay for 5 months.

I just asked my mom about the medical insurance and she said that she got it covered. Is there anything else that I need to know? Any documents that I miss? Or any reason for the IO to deny me?

Thank you all so much. I really appreciate it.

By the way, if anyone's curious as to why I'm staying there for that long, I want to keep my aunt company for awhile since she lives there alone now. Her husband died and they had no kids.

Trouble is, that might sound a bit open-ended, notwithstanding everything else. I think you would need to make sure that anything you have in writing about this from your aunt makes it clear this is a commitment to a limited amount of time.

And you are going to check the details on the health insurance yourself, aren't you?

Yes, I will check on the health insurance myself.

For the health insurance you need to be prepared to pay the bills yourself and then submit to the health insurance company for reimbursement. EVen if a plan covers you outside the UK the practitioners/hospitals in the UK won;t take any US insurance. All the card will do is show that you have coverage to be reimbursed.

No worries--given your return ticket and under 6 months visa no one will bother you about medical coverage unless you need it and then you will be charged (but free ER visit!). Given you have an address and relative to stay with you will be fine.
Where are you headed? What will you do? Sounds like a great trip!

@nytraveler Thank you for letting me know

@opus I'm headed to Glasgow I'm just going to chill there, it's like a trip before conquering college lol and to be honest.. I'm actually trying to escape winter here! (I live in one of the coldest states, if not the coldest.. I promise to make a trip report once I get there. My aunt said she would tour me around... I told her I want to go to Paris! (Like every other teens out there lol) I have to do research about Schengen but I'll do that later.

" Chill" is the operative word here!
You are going to Glasgow in October for 5 months to escape the winter?
Bit more research to do I think!

You might want to check about leaving Qatar airport airside:

http://travel.state.gov/travel/cis_pa_tw/cis/cis_1003.html#entry_requirements

Shouldn't be an issue but may cost a bit.

If you plan to visit Paris during your stay in Glasgow, no problem, assuming it's not for longer than 90 days!!

Honja wrote: "I'm actually trying to escape winter here! (I live in one of the coldest states, if not the coldest.. "

North Dakota, maybe?

Frances wrote: "You are going to Glasgow in October for 5 months to escape the winter?
Bit more research to do I think!"

Frances, if honja lives in one of the coldest US states, she will be escaping the winter in Glasgow, which has never had temperatures of -30° F to the best of my knowledge.

But also: short days (Glasgow is further north than Labrador, Banff and Beaver, Saskatchewan), and lots of rain from the Atlantic.

That's the catch — the wind and rain! But where I grew up it was rarely warm enough in winter to have rain.

also, i would have my aunt's phone no available so that if immigration want to phone her and check up, you've got the number handy for them.

good luck and i hope you have a great time!

I don't understand your graduation, SAT, college application process.
Don't most school graduate in May or June?
If you are applying to start college in Fall 2013 you would need to take the SAT before you return from your trip. Depending on where you are applying, college applications are due way before you will return from your trip.

I just wouldn't want you to miss your deadlines for college applications.
Have a good trip.

Everyone ....... I live in Alaska lol

@annhig I will! Thanks

@meadeparsons Hi, I'm going to take the first SAT examination on October 6th, the day after that will be the day I leave home. The reason why I stated that I have to be back for SAT is because I want to take it twice. I must take it twice. I'm quite sure I'm not going to do well on the first one :/

Alaska! Haha, I was thinking of the coldest state in the lower 48! Glasgow will be positively balmy, and the days longer than you are used to in winter.