It's definitely
around WWI. I'd venture a guess of 1919 based on the design of the front forks.
The problem is that from 1900-1925 there were about 5,000 little motorcycle companies in the US that disappeared in the depression. Most of them you've never heard of. Could be a Yale, could be a Pope, could be a New Hudson Autocycle. Hell, it could even be a Harley Davidson or an Indian. They all looked pretty much the same.
It should have some information down on the crankcase cover, however. But be aware that the name on the engine may not be the name of the actual bike mfg. Most of those little companies used bought-in engines. It looks like the typical engine of it's day: an IOE two-stroke, probably 1000cc's, maybe 3.5 HP. Quite the screamer for that era!
Documentation will be scarce to non existant (unless it is one of the more popular brands) and it looks like it's missing a LOT of bits that you will NEVER find, so if you are planning on running it get friendly with the local fabrication shop.
The market for something like this is going to be pretty small. What is he asking & how deep are your pockets?
Put some bicycle tires on it, paint it a pretty cream color & hang it on your wall in the garage.
-JP