I also checked the oil, and it was fine. The air filter also looked clean.

Identifying the engine could be useful!

Try priming the carb with a couple teaspoons worth of gas.

Sometimes, a liberal shot of starting fluid will help to wake it up. Thats what i use in the Spring, after winter storage.
Although: If you had it stored in an outside shed or garage, the resident mice may have made a home in the flywheel area of the engine. They just love to make their home under the round tin flywheel cover on the engine. They are safe there from cats and other creatures that would like to have them in for dinner! They also seem to relish the taste of the main spark plug wire insulation, as i have found those wires gnawed bare, That kills the spark as effectivly as turning off the key. If you find that situation, you will have to clean out around the fins, and down in their toilet hole. A good strong blow out with compressed air will usually suffice!

Rusty!!! With all due deference to yer age/experience, starting fluid is not good for small gasoline engines. Mownie will haunt you. Rattlecan carb cleaner is a better choice - much less chance of engine damage.
Needless to say, all the rest of yer advice is spot on...

Yep, unless you have a heavy duty Cummins diesel on yer tractor............keep yer diethyl ether starter fluid on yer shelf.
In all fairness though, and to clarify somewhat, The use of ether based starting fluid in all kinds of gasoline powered engines is NOT AS LIKELY to cause damage if used sparingly when the temperatures of the engine and ambient air are 20 degrees Fahrenheit or colder.
The explosive blast that can break piston rings and stress other parts is less apt to occur when the temperatures are that cold.
Where people stand the most risk of doing damage is when they use ether starting fluid at higher ambient temperatures or they feed it to an engine that has already been run and warmed up. Another factor that can increase the risk of damage from ether is is the spark timing. If there is a condition/defect causing the spark to occur earlier than normal...........the chances of breaking things increases significantly.
A shot of the commercially available spray can carb cleaner is much gentler on the engine than ether.
It comes down to this: Diesel engines are built a lot heavier and designed to handle much higher combustion chamber pressures than a paltry little gasoline powered engine.
A shot of ether exploding in a diesel engine is like a firecracker to that engine.
A shot of ether exploding in a gasoline engine is more akin to dynamite.

It's best to use a gas stabilizer in the gas tank before storing for awhile. Or drain it out completely including carb. Stored gas for several months gums up and will interfere with proper carb function. It can get so gummed up a carb cleaning may be required. Every spring, I get calls to ungum a carb where the owner neglects to use a gas stabilizer.