No, you can try to learn on a smaller board. But it will take much longer. A length of the board equals glide and momentum. The longer the glide the more time you have to get to your feet. The more times you get to your feet the faster it becomes muscle memory.
Kids under the age of 12 will have an easier time trying to learn on a shortboard. Mostly because they are lighter and have more energy. The tend to be more resilient and will not get discouraged easily.