I don't believe in age barriers. the minute you start thinking about age is the minute you start limiting yourself. Life is short and one should pursue their dreams regardless of age.
Starting a new career, pursuing an education, marrying the one of your dreams, traveling the world; whatever your dream, it's never too late so long as you have life.
Go for it! I resigned my job to work full time from home at the age of 40 and has not regretted a day.
The reality would be the type of career as some companies want younger people these days. If you are starting your own business then by all means. Do your market research and figure the best way forward.