Have you scanned the vehicle?
What is the history on the vehicle?
Mileage, recent trans repair work or service?
If the speed-O ias not working the system does not knwo the vehicle is moving... since you say the speed-O works, there is another test
You can unplug the trans connector at the case or remove the trans fuse in the panel. This will put the trans into default - fail safe mode. The trans will then be in 3rd gear and would not want to move from a full stop without lots of throttle applied.
That will at least tell you the 3-4 clutch pack is good
In manual 2nd gear, the trans is not in 2nd gear?
Dont worry how old you are... it is the mileage on your body that adds up.