How long does it take to learn Tabla?

Tabla is a lifelong journey, so the learning never stops. So the answer depends on what your goal is, how much effort you are willing to put in practicing and who is helping you in the journey of learning Tabla. 

A lot of people I teach, like to accompany Bhajans and simple songs. That is a clear goal. If you are able to devote 30 mins a day or approximately 3.5 hours a week, you should be able to accompany with a simple rhythm on slow Bhajans and simple songs. There will obviously be a difference in the quality of the rhythm whether you have spent 3 months versus 3 years learning Tabla. But as long as you can enjoy even simple beats, this should not be a hurdle for you. Over the period of time you will continue to improve.

If you have a goal of being able to play some interesting compositions, playing for 3.5 hours a week will take you around 2 to 3 years. Again, you may not be able to play like a thorough professional, but good enough to enjoy the composition yourself and add some when you accompany it with songs. The Tabla for Beginners course series is what I would recommend for you to start learning Tabla.  

If you want to play in an intricate and traditional solo format for 20 mins on stage, it will take at least 5 hours of practice every week or 40 mins every day for around 4 to 5 years to get there. Again, the quality of the sound and compositions will continue to improve as you keep adding practice time or practicing for a few more years. 

Most of these answers are for adults or late teens who would like to start learning. These goals will keep you motivated along the way. I suggest that children in their early ages SHOULD go for the traditional learning Tabla. They have time on their hand, learnability is high and they have a very high chance to achieve proficiency as long as they are consistent. I hope this has helped you make up your mind to get started with Tabla.