One of the most discouraging aspects of growing older is reduced memory access, short-term memory in particular which can make learning a longer path. But with age also comes thinking balance, insight balanced against experience resulting in learning the concepts of a new subject just as effectively or more so than a young brain which lacks experience. For example learning a new language is much much harder as one ages, and in fact gets progressively harder after age 7 or so(western schools have foreign language classes AFTER the brain physiology has changed that reduce the language acquisition ability significantly. Languages, art and music are really best started during first language acquisition around 2 years to 7. After that and the brain is not well suited to learning symbolic languages of music, symbolic math and languages.
For older people in western societies, the important element missing that maintains brain effectiveness is thought stimulus. Most people get into a routine that does not require thought, such as work, home maintenance, engagement with others etc, and way too much time is spent doing routine actions and watching way too much TV while their brain function atrophies. Getting rid of TV and engaging in the community doing things never done before, engaging people doing things never experienced or learned before, being around active young people, or people from cultures they have never interacted with before, or going to live in a fully new environment, a new country etc keep the brain learning to make new connections. Routine and lack of stimuli makes learning new subjects really hard. TV is probably the biggest killer of thinking and brain function ever invented. Travel is a good stimulus but only if getting out of routines that are too comfortable. Backpacking through Asia or South America is much better or brain exercise than say, going on a cruise which is very set in a routine.