My son is using El Capitan on a Mid-2010 MacBook (white unibody). He uses it to play Minecraft (Java) and in the remaining time do some homework.
Initially, EC was slow: opening Preferences took ages. Then I took the MacBook to LEAPP (an anagram of Apple) and they installed 2x 4 GB (for € 80,00) in it. Now it's fast again.
Note that this must be: Late-2009