The author on her Harley. (Photo credit: John Livzey) We should avoid excess risk as we age. So says conventional wisdom. After all, it takes longer to heal a bone broken learning to ski in our 50s than in our 20s. There won’t be time to regain a financial loss suffered past our early 40s if we become too aggressive with our investments. Going back to school later in life to embark on a new career seems a waste of time and energy. And don’t get me started on those folks who leave long-term marriages for the greener pastures of a new relationship. I believed all these things. Until, at age 48, I fell in love with a matte black, brawny beast of a machine. I took a motorcycle safety class as research for a book I was writing and surprised myself with the depth of feeling that burbled up. My father was dying at the time and I felt entombed in a marriage that, after 25 years, had lost all its verve. I had …