One possibility is a worn out battery. Even after charging, the battery no longer has the capacity to deliver crankiing power. The clue is in your statement "It first started with a jump only".

Another possibility is resistance in the wire connections. Disconnect the battery to avoid sparks. Clean all the ends of the wire by wire brushing. With the battery wires removed, use a wire brush to clean the connection points on the wires. Clean the posts on the starter solenoid and the starter. The battery ground wire usually bolts to the mower frame. Even if this is tight, there may be resistance. Loosen the frame screw, clean and resecure. Tighten the engine mount bolts since they complete the electrical circuit.

A third possibility is the grade of engine oil. SAE 30 is specified for hot weather. SAE 10W30 is ok for cooler weather.

A fourth possibility is a dragging starter.

A fifth possibility is excessive compression from carbon in the cylinder heads. Valve clearance also affects compression.

The last two items are usually more work than more home owners want to attempt.

I for one, am NOT going to bounce back and forth between 2 threads on the same tractor.
Especially after you asked and were advised NOT to start a 2nd thread!

Bye-