Your CPU should support the 64bit length which btw is supported my most processors now. To be sure install GRC | SecurAble: Determine Processor Security Features | and check the Max bit length if it shows 64 then you can run a x64 OS. Generally windows x64 is used to support RAM memory over 3GB
In earlier days, days of celeron 1st gen. You had 32bit CPUS. Now most of all CPU are 64bit.
64bit cpu can run 32bit os as well as 64 bit os. If you want to have max cpu power, use 64bit os. But if you have 2GB ram (Idk why in 2K18) then gofor 32bit as it is light on RAM.
32 bit CPU cant run 64bit os, so there is no choice.