Aside from only being 6 foot that is pretty much me - can eat anything I like, as much as I like zero weight gain but I don't lose weight if I barely eat either. I carry pretty much no fat but easily bulk up if active. Don't have any symptoms really that would indicate an overactive thyroid though atleast not so far though I had a colleague who was similar then went full on symptoms of overactive thyroid when they hit ~50 which forced them to take early retirement though they seem to have got it in control now they aren't working.
The doctor i went to see did a simple test , he told me to hold out my hands put a sheet of paper on top of them , watched it for a bit and pretty much told me there what it was , had a blood test , couple of days later was called in to see him , told me what tablets he was going to try and sent me for a cardiogram.
Got to take the tablets for 18 months have a blood test every 3 months to see if they are working if not then its operation time .
Symptoms i had where :
Hand and leg Shakes , standing still in a queue and my legs would start shaking
Heart would suddenly jump from a steady 45 bpm to over 100bpm for no reason
Think it steadily got worse when i was around 45 , missus told me last year that she thought something was wrong (i actually already thought it was parkinsons Disease).
Now my sister who i only saw last year for the first time in 5 years , said she was actually on antidepressants and couldnt understand why as her homelife was all good and was diagnosed with an Underactive Thyroid but had no outward symptoms like the shakes.