Four 70 year olds were planning a 4 night visit to Rome but most of the information seemed to apply to energetic youngsters who planned to see Rome on foot.  Here are a few tips for the more mature, but reasonably fit traveller.  The hotels near the centre are convenient but quite expensive, whereas those a little further out are better value particularly if they are close to a Metro Station with fast cheap links around the city.  The Roma Pass may be good value if paying full price to enter the Colosseum and Roman Forum but a better alternative for the 65+ year olds is the Roma Christina / Metro / Public Bus combined 3 day ticket for 25 euro.  These tickets can be bought on the Hop on Hop Off (HOHO) Yellow Double Decker buses.  The traveler then has the option to use all 3 systems - the HOHO offers a good commentary and view but is slow in the traffic, the Metro is easy and fast but does not go to several sites, and the public bus is flexible but a little more confusing.  Do pre-book entry to the Colosseum on the internet asking for Complimentary Tickets -  works well.  9am is a good time to enter as it opens and do not forget to go to the pre-booked window where the queues are much shorter.  The audio tour hire is worthwhile.  The Vatican museum is also best pre-booked on the Vatican Web (9am is again a good time) which lets you walk on the Right hand side bypassing the very long queues.  After the Vatican you can walk round to St Peters Basilica where again there are queues for the free entry but they move quickly and the wait is worth it.  An itinerary that worked well and was kind on the feet was:

Arrived mid pm and did a full tour on Roma Christina HOHO without getting off.  This takes just under 2 hours and give a good over-view.

Day 1. Taxi to Colosseum, then walked to Roman Forum and Piazza Venezia.  HOHO to hotel.

Day 2. Metro to Vatican/St Peter Basillica . HOHO to Piazza Navona then walk to Campo di Flori and HOHO to Trevi Fountain.

Day 3. Metro to Republica to see Santa Maria degli Angelica Basillica, then Metro to Spagna (Spanish Steps), then Metro to Flaminio to see Piazza Del Popolo and Santa Maria del Popolo Church, and a taxi to Pantheon.