I often hear people ask the question, "how long does it take to get good at martial arts?" It seems like a fairly straight forward question but more information is necessary to answer it. Usually, people have some mental image, implicit or explicit, of what they think being "good" at martial arts looks like. It goes back to what your goals are.
Do you want to be the best fighter in the world? Well, that'll likely take a lifetime of training and you might not even achieve it.
Do you want to be able to win competitions on an international scale? It'll take several years of dedicated work.
Do you just want to be able to handle the average angry drunk at a night club? That'll take a lot less work than the scenarios above.
I like to think of it in terms of the entire population of the world. If I were in a fight with another person selected at random, what's the percentage chance that I have the skill, ability, and luck combination to beat that person? For me, if I can have a better than 80-90% chance of winning (and I think I do), then I consider myself "good". Maybe 90% isn't acceptable to you. Everyone has to make that decision for themselves.
All this being said, individual talent and athleticism is certainly a factor in how long it takes to achieve proficiency in martial arts. So, take an honest assessment of yourself, make your goals explicit, and then decide whether or not you have the requisite patience to achieve your goal.