No. It is never too late to start learning an instrument. It is of course true that a small child will learn faster and more effortlessly than someone with a mortgage, and that one’s potential to achieve a very high level of ability diminishes with time, but these differentials should not discourage an older student unless their heart is set on becoming the next Horowitz or Stevie Wonder.
In reality an adult can improve greatly given discipline and time, especially since most adults have one major advantage over children: they know how to learn and how to research. A child’s memory is unparalleled, but most children do not know what questions to ask during a lesson, how to practice efficiently, nor how to locate helpful resources in a library or online. An enthusiastic adult learner who makes time to practice every day will invariably improve if they go into their practice sessions with a positive as opposed to a despairing attitude.
Remember that the make of a musician is not necessarily the sum of their powers of memory and technical prowess. Horace Parlan and Mal Waldron were not savants like Art Tatum or Keith Jarrett, but their music is not necessarily less enjoyable.