Welcome to the forum!
That's quite a disaster, but apparently the interior is better than the outside since the action seems to work and you can cock the hammer. That's a good thing.
I presume there's no cartridges in the cylinder chambers.
Yes it's a hundred years old, the serial # which is the #157XXX does not lie. Guns of its age are shot and enjoyed every day in this country.
The cartridge roll mark on the barrel of that vintage actually reads: ".32 Long CTG" and it's still available. All of these take 6 rounds. But it's a premium model because it's a target model with adjustable sights, that makes it a bit rare.
I'm happy to hear that you would like to clean it up and hope dad gives his permission (after reading your thread here, perhaps). But the next move can either ruin it or rescue it.
The worst thing you could do is start physically cleaning; no steel wool, wire wheeling it or scraping off the rust!
The 1st thing is to put a little lubricant on the ends of the two grip screws, let soak, and then remove the screws and grips, and set them aside.
The 2nd thing is to immerse and soak the entire gun in rust remover (do not attempt to disassemble it!). The two best products are:
1. A 50/50 mix of automotive transmission fluid (ATF) and acetone. The soaking container must be sealed or the acetone will evaporate very quickly.
OR
2. "Eastwood Rust Dissolver"
YouTube
Don't waste money on any other products.
3. Soak until all visible rust is gone. Try the action in both single and double action. If that works, attempt to swing out the cylinder from the left side by pushing the cyl release button on the left side forward. If either one or the other doesn't work, soak again.
4. Once the parts will work: Rinse away remaining product with water, squirting it into the action thru all openings. Wipe it dry and let the inside drip dry. Then spray with an aerosol gun lubricating product from a gun or hardware store, Walmart, or Amazon on-line if there are no stores open in your area.
5. Report back here with some photos and we can walk you thru some next steps like safety checks or further restoration before you shoot it.
Have fun and don't be in a hurry.