Is the Magikarp that you can buy from the Rocket in the Mount Moon Pokemon Center worth it for an early game Gyarados? Or should I wait until I got the Old Rod....and when is that?

If you plan on training a Gyarados, then yes; 500 money is not an awful lot. I got it to evolve to a Gyarados right after I beat Gary on the S.S. Anne. I never ended up using the Gyarados, but it was still good Dex data.

I don't even remember ever using the Old Rod, ever.

It's not a bad deal, no. Plus, you can save and then reset until you get a good nature and DVs.

I was originally seriously thinking about this, but then I forgot about this topic, and went through Mt. Moon. I have to start reseting about 50 times to get Nuggets from Nugget Bridge so I can buy a ton of stuff at the Game Corner (Dratini, Ice Beam, Flame Thrower, T-Bolt) and to have plenty of money to buy proteins because my Charmeleon's attack stat is the lowest. It's hasty and extremely fast, and I don't care about DVs. But I do care about nature...

Anyway, I found out that the Old Rod can be obtained in Vermilion so I decided it's okay. I think there's some water in Vermilion that's accessable so I'll just fish for 'karp there and train it on the SS Anne.

Thanks to both of you, but this can be locked.