How long can my african cichlids live in my 35 gallon tank? please answer?

I have 21 african cichlids in a 35 gallon tank, they are babies about 1.5 to 2.5 inches long. I have talked to a fish expert near me and he said they can live in it forever, but I just don't see that happening. My filtration is a fluval fx5 and I also have a bubbler in the tank. I am looking for a time frame so I can know how quick I need to save up to get a bigger tank. Thank you for your help.