If you can run 55 you ought to be able to run under 5. If you can run 2:11 you ought to be able to. However, a 55/2:11 combo indicates a serious lack of endurance. At 55, you should be somewhere between 2:00-2:05. Heck, I was a 54/1:58 in HS (but I ran 4:14).
Can you work on your endurance? Sure, but only so far. Still, I'd think you should be able to run sub 5:00. You need to run slower mileage. Keep your heart rate in the 185-age range and put in a good 50 or so miles a week. DO NOT neglect your speed. Do short sprints 2-3 times a week near max speed after some of your runs. You just need to do 6-8 X 50-75yards.
After 2-3 months, you should be running faster at the same effort. You can run a test once every 2-3 weeks. Run a mile at that same easy pulse rate. You're time should be getting faster.
If you are making progress, then start adding a tempo run once a week. 2-3 miles at 85% max heart rate. A month or so after that add intervals. Start with 3-4 X 1000 in addition to the tempo run. After a few weeks drop the tempo and add another session of 8x400 at mile pace. A few weeks later drop the longer intervals and add 15X200 at faster than mile pace.
This should get you ready. Whether you can break 5 after 4-5 months at age 29 in another story, but I will say 29 is NOT too old. However, you are getting close to where you will start slowing down. It happens to us all. Endurance should last longer, but speed goes in your 30's for most of us.