There is a good chance it was stored with fuel in the tank and/or carburetor, and the petrol has evaporated leaving oil, which has plugged the main jet and perhaps some other bits as well. Does the carburetor have a flood button (which pushes the float down, thus allowing the float bowl to over-fill, so fuel runs out a small hole in the top of the bowl)? If it does, you can use that to check whether fuel is flowing into the float bowl and whether the needle and seat are working properly. Have you tried removing the spark plug and squirting a few millilitres of 2-stroke fuel (not straight petrol) through the plug hole, then reinstalling the plug and its lead, opening the throttle, and pulling the starter? If it has spark and compression, it should start and run for just a few seconds. Once you've established that it can run in that way, we can talk about a process for cleaning the tank, fuel line and carburetor, and assessing the compression.
I suggest you go carefully to avoid damaging the mower in these early stages. Never put unmixed petrol in the mower, and be thoughtful and gentle, always using the right tool when you dismantle bits of it. Anyone can make a mess, but it takes a responsible person to take care of old equipment and ensure it gets better, not worse, while in his or her care.
