Typically, it takes roughly 6-10 years on average to earn a black belt judo as an adult. With consistent judo practice of two to three times a week it is realist to achieve a black belt during this time span.
The difference between aikido and juo is that Judo is a competitive martial art that includes live sparring and techniques used against fully resisting partners. It focuses on standing throws, sweeps, and take downs with some ground work submissions. It is very effective for self defense.
Modern Aikido is a non-competitive martial art that has not been proven to be effective as a martial art or as a self defense system. Aikido training involves practicing movements like throws and holds on a willing partner and does not involve any live sparring.