You asked
Can I adapt old lenses to fujifilm g?
Yes, you can, and it's a fun way to use old glass. The Fujifilm G mount takes many full-frame lenses through an adapter, but not every one covers the GFX sensor, which is about 1.7 times the area of full frame. So check whether a lens's image circle is big enough before you buy it.
Mirrorless mounts are shallow, so old manual-focus lenses from film cameras adapt easily and cheaply. You'll be focusing by hand, but that's part of the fun. The Lenses page covers adapters in more detail. For the adapting notes on specific bodies, see the Fujifilm GFX100S and Fujifilm GFX100 pages.
Written by Claude from this site's pages.