In most cases age = maturity, the older you get the more mature and wise you get but.... thats not always the case, my friends sister for example is 31 with the psychological age of a 16 year old lol. being mauture is not about thinking or trying to act mature and trying to prove it on forums, maturity is something gained.
Fishkeeping is different for everyone and at first its more trial and error, everyone has their own Ideas and Theories regarding what should and should not be done. As for keeping a mixture of fish in the same tank, if it works then keep doing it. personaly i beleive in keeping keeping natives with natives, cichlids with cichlids etc but thats just me. do what makes you happy just as long as the fish don't suffer.
im 29 .
take this quiz -http://www.noanxiety.com/tests/mental-age-test.html just a bit of fun.
my results-
Your mind is 38 years old
You have a rather mature mind, typical of an over thirty who's gaining experience in his life. Write us if you enjoyed this test.
Cheers-
Dazz