Absolutely NOT! In fact, quite the contrary.
Although you may feel that you don't learn as fast as you used to do, many recent scientific studies have shown that older people can obtain long term results that are just as good as younger learners. Want proof? Swedish scientists
tested a group of younger (21-30) and older (65-80) adults for 6 months and ‘did not detect any significant age-related differences in plasticity of white-matter microstructure’. Translation:
older brains adapt to learning environments just as well as younger brains do. Not convinced yet? This study from MIT
shows that a group of adult students learning Chinese were tested over a nine-month period, during which they showed ‘improved white-matter integrity’. Yes! That white matter is what connects neural cells, so the better connected, the better you can accomplish a cognitive task. In conclusion, the more you challenge your brain, the better it will become at adapting and succeeding at learning.