Transmission Question

I have a 94 Geo Metro with a manual 5 speed transmission. It shifts fine from 1st to the 5th whether moving or not. What is strange is that while driving I can down shift from 5th to 4th to 3rd with no problem. I cannot downshift to 2nd unless I travel less than 12mph and for 1st it has to be completely stopped. Of course I have to double clutch for those gears. Somebody told me that it may be a special lockout to prevent over-reving the engine. Or is it some synchro mesh thing I have been hearing about.

That's a worn synchro. I would take it easy on the tranny, before you lost 2nd gear completely. Metro transmissions have a bad habit of wearing out the 2nd gear synchro at around 130-150k.