The old rod is useless, unless you want a Magikarp or a Feebas.
The building is on Route 218.
Old Rod- You know the building where you can enter and exit canalave City. Talk to the fisherman. He will ask you if you like the old rod. Say yes.
You get the old rod to the left of jubilife city.
There is none there only old rod good rod and a super rod
Old Rod.
Magikarp
I think u mean old rod, and if yes, left in the small building from jubilife city, talk to the fisherman and agree on whatever he says
West of jubilife city.
You can catch them if you use your old rod in water.
battles,water with old rod
in jubelive city go to the left the you will come in a small building talk with the fisher he will give you an old rod to get the good rod you have to be under soleceon town there is another fisher talk to him and you Will get a good rod to get a super rod go to the battle frontier with the ship go up (after national Dex XD) and talk to the fisher you will get the super rod
Old rod= Route 218 Good Rod=Route 209 Super Rod=Get the National Dex, found in the Fight Area.
When facing water, open the [START] menu using the 'X' button, then go to [ITEMS]. After that, select [KEY ITEMS] and then the [OLD ROD].