I just finished your personalized profile and it said my target heart rate for exercise was 86-112. My doctor told me to use 120-155 as my target heart rate. I've been doing this for the past 7 months. The 86-112 seems way too low to me. Remember the calculation is a statistical projection.
Every individual is unique.
Since you are able to exercise at a pace higher than predicted, you very well could resemble a younger person, or are more fit than the profile predicted. I personally advocate using the age you resemble as opposed to literal age. We are still building the profile. For weight gain, we will have two components which you, as a personal trainer might appreciate. The profiles are based on thousands of people who have take health risk assessments as well as stress test and predicted pace for range of target heart rates.