I'm not sure what "fit to be a developer" means. People (with very few exceptions) are not born with labels that say "able to write software professionally" or "not able to write software professionally". Try to understand what has prevented you from landing jobs so far. Go through http://sijinjoseph.com/programmer-competency-matrix/ to determine what you lack, and then work on improving those. (Not saying that that link is the ultimate criteria for determining one's suitability as a programmer, just that if you really don't know what you're missing, it will give you some ideas)