2strokenewb...  USA did not officially get a Yamaha 125 Enduro without electric start until the new monoshock model in 1978.

Kick only models in the US could be the "MX"...  someone "might" have converted a 12v generator/starter model to a 6v magneto (quite a bit of work, wiring harness and a lot of parts need to be changed)...  someone might have installed a Powerdynamo 12v magneto (or equivalent aftermarket magneto to replace the starter/generator)...  someone could have served in the military and brought a non-US model home with them...  just to name a few.

It also would not be unheard of to find a starter button missing (or removed by a seller because e-start doesn't work)...  of course that makes it "kick start only" but it's still a 12v starter/generator model.  

This page says mine is a USA model by VIN, and it does not look like it's been converted. I will have to do some more investigation. www.legends-yamaha-enduros.com/vin-numbe...jLdSHAtlQ7u-HQd419XR

Well, I figured it out. It just does have electric start. only clicks the solenoid and just barely turns the engine

Ok that's good, now were on the right track.
If it runs & the battery has water [if that type] then you'll see it charging by shining the headlight on the wall in the dark & with it at a slow idle it'll dull a bit then come up at just above idle & hold as revs increase.
If nothing changes then i'd look at brushes although if starter is trying to turn then maybe not brushes & might be just an old battery past its "useby".
If you have a DC volt meter across the battery then should see the voltage rise above idle but headlight idea is easy to do--can hear it charge 'if it is' as it struggles a little as it cuts in--electric brake.