japanese living

I'm a 16 yr old and i've been wating to go to japan for a long time. Anyway, i was thinking that i would need about 6000-5500USD for the 3 months i would be there. which inculdes my rent(120,000 Y a month) and misc expenses. But i feel that i might need more because i also want to spend sometime in Seoul. i was wondering if someone could tell me their average expense what their life is like. (btw im black)

despite being more privileged. my parents r making me pay for the 2500 on my on. so i won't be able to go to tokyo till im 18.

i spent 3 months in tokyo 2 years ago. including airfare i spent AUD$7000 which is about US$6500. My rent was only 55 000 per month.

It is pretty hard to give a figure as it all depends on how frugal you are. At the same time you do need to go out of Tokyo, if only on week -ends, and you may want to buy "stuff" like electronic devices or clothes etc.
for tourists it is often suggested that they budget at least 5000-6000 yen a day for 3 inexpensive meals,entrance to temples,museums,and local trains or subways. Multiply by 90 days to give you a rough idea.
food is expensive, especially if you want to have the food you are used to back home. Fortunately you can have cheap meals (rice or noodle with either meat or fish) in small restaurants found near railway/subway stations. Of course you can cook at home, if you have a kitchen, but again,supermarkets,grocery stores etc. aren't cheap (I am comparing North America, where I live, to Europe and Japan where my partner and I have families. Their food bills are huge compared to ours back home)
you will also have to buy commuter passes to travel daily around Tokyo. check www. urbanrail.net (click on Asia then, on the map, on Tokyo to see the subway map and the fares).
It is more than likely that your parents make you pay part of your expenses because they know that you will be more careful if the money you spent is (partly) yours. They also know that they may have to give you an emergency loan at the end...
Have fun and please let us know about your experiences when you come back.

What will you be doing in those 3 months, just living in one place?

I kind of gets boring after a while if you're not actually doing something, like going to school, work etc. something productive.

Of course if you spend time in South Korea you will need more money.