In only six short years (at the very earliest), you can take the Minuteman Trail from Bedford to Alewife to Davis and the Somerville Community Path from Davis to Lechmere. The Minuteman exists and the Community Path exists up to Cedar Street, just short of the new Lowell Street station. From there to Lechmere will be new trail following the upcoming Green Line Extension. I'll be over 60, but I'm looking forward to when I can skate from my home in Arlington to the Esplanade in Boston.
Read more about the project on the Arlington Patch ("State Announces 1.9 Mile, $39 Million Path Along Green Line Extension Project") or in The Boston Globe ("Somerville bike pathway to expand").