Of course you can- presuming your parents have given you permission. One thing to watch out for though is 21L-ish tanks which are said to be big enough for 2 goldfish- they arent. Goldfish can get bigger than most people think. I'd reccomend at least 60L for 2 or 3, so you're going to need a decent amount of space for a decent sized tank.
Hope I helped :)
I have 5 fishtanks in my room, none currently hold goldfish, but one tank is going to once I change a few things and switch around a few fish.
the problem is whether or not you have enough room for a goldfish tank. goldfish are really messy and get really big. so for one of those fat, round goldfish (fancy goldifsh) you need at least 20gallons (75litres) for the first and 10gallons (40litres) for each additional goldifsh.
so, if you have enough space, money, and time for care, do a little more research on they type of goldfish you want and fishless cycling, and go for it. I find my tanks very relaxing.
Unless you spend a lot of time in your room they may be better off in an area where they have a lot of space and can be enjoyed. A couple of fish can be put into a small tank but the main thing is using a filter to aerate the tank. Goldfish are heavy polluters and although they can tolerate temperature changes more than some other fish, clean water is very important.
Having them in your room may not bother you at all, but the filter will hum all through the night and may disturb you!
I will assume you have your parents permission and a tank large enough and filtered. Be sure to turn off all lights at night. Fish need sleep also. You will still have to do water changes weekly.
If you like. Just make sure that they are in a sufficiently large tank, and don't take them to bed with you.
They need water.
Of course you can but make sure to clear a big space on a table or desk and ask your parents if you can get some fish.