Complex sentence: At the age of 27 he was a star of the New Hampshire Democratic Party, although his personal life was nowhere near as successful--in his personal letters he continued to lament his bachelorhood and yearned for a life beyond Hillsborough.
Split into simpler sentences: At the age of 27 he was a star of the New Hampshire Democratic Party. There with taming early political and professional success, in his personal letters he continued to lament his bachelorhood and yearned for a life beyond Hillsborough.