Fast heart rate around 100-110 bpm. Healthy and active, limited caffeine use, normal blood tests, EKG for heart murmur when I was young was normal??

Possibly. Having a slightly high heart rate with no other symptoms could be normal or due to anxiety. Granted you had an EKG when you were younger it might be wise to see your doctor if recheck of that would be indicated. Good luck.
Tachycardia. You always have a fast heart rate? How often have you measured this? Do you measure it for a full minute? Most people have a heart rate between 60-100 at rest. You may wish to measure yours a bit more before deciding it is time to check again at the doctor. Your past history sounds good- no concerns there. If you have a fast heart rate all the time, it would be a good idea to have a check up.