I have a 1991 Yamaha FZR 600. One day I went out to my bike after not driving it for four days and the oil indicator showed no oil and yet there was none on the ground? I put a quart in and drove it and once I shut the bike off it started leaking oil and consistently did when I was riding. Is this a gasket problem or do I need a full oil change done because i dont know the last time it was done since i bought it a two months ago..

You have put a quarter of a gallon (1.3L) as a top up in an engine that only has around 4.5L in total capacity.
You have ended up overfilling it and the excess crankcase pressure is pushing the oil out the breather pipe.
If you don't have the right amount inn (either too low or too much) you will do damage. Too much oil can push past seals and damage components, or push past the rings and end up in the compression chamber, with potentially disasterous results - everything from a fouled plug to a holed piston to a broken big end bearing or crank.
The only way to be sure is to drain the oil completely and refill with the correct amount - may as well replace the filter while you are at it - your bike will appreciate it - just remeber to allow an extra 250ml for the oil in the filter.

I would get a full oil change. It will thank you regardless. The oil light may just be a simple electrical fault, bad connection etc, or maybe it has always been low and the angle you parked it at showed the switch better.
If you by a bike you don't know if it sat or what change the oil the clutch will work better, ensures better protection for the cams, and then you know what you got. If the bike still leaks after the oil change then it's a gasket or seal somewhere find out hwre its coming from then deal with it. hope this helps