Good call, wasn't thinking about the age aspect, just playing devil's advocate with the whole thing. On that note though, any AAS would/should fall into the same boat. I'll give you this part, but do take issue with the rest of your post:
So which sides might be permanent? Sweating? Also which of these is going to be experienced at 50mcg/day? Which one's that might be experienced at said dose are going to be worse that other things commonly excepted for use in fatloss?
Well, that is why one would use it.... misused - that's the result one would want IF used correctly.
Please tell us more about how sensible use would cause permanent thyroid deficiency, or how at any dose the risk is greater or more likely than with... Let's say Anavar? I like to err on the side of caution, but to take issue with an idea and use scare tactics and nonsense for support isn't playing fair. So to be simple: Please show me how using exogenous thyroid puts one at more of a risk of damage than using exogenous testosterone.
I can't/won't argue with the 20 year's old part, but the rest of your post is totally 'chicken little'. I find it funny that many will suggest running an somewhat heavy steroid cycle, but 50mcg/day Cytomel is bad? Or especially the fools that suggest not running AI's for support/control for "optimal" gains, but would also take issue with 50mcg/day Cytomel.
Overall, I think you are right in not suggesting the use of Cytomel for an 20 year old. I did speak from more of an 'optimal' results aspect without age as an thought. With Cytomel use, just as with AAS - one should have an thouough understanding of what they are doing before they do. AAS is so often misused and misunderstood without much thought into the foolish ideas/suggestions given and taken: I would argue that AAS use, as is often reoommended, is far likelier to cause damage than sensible thyroid usage - it's just with thyroid usage we quote one person for our backing, while we sensilessly debate about optimal muscle gain with no logical thought into the damage that one is doing.
This is a board to discuss steroids and there uses, but you're right: Thyroid use does have the potential for sides and is very easily abused. Albuterol comes with it's problems and no one can argue that it would be healthy. Any of the AAS also come with their list of sides and extreme ease of abuse potential and serious health risks beyond shutdown. Maybe I should only suggest 100% safe methods and not bother posting in this forum and stick to the Bodybuilding and Nutrition forums as nothing in this forum comes without risks of some sort... But I'm getting of track: The age issue is the only part that I will retract my statements on, and is a very important aspect when giving advice or opinion and is something that I ignored... I guess I blew off the background back when I got hung up and blew off on how phenominally huge and musclar the OP was to begin with. So: Given the age, my suggestions aren't taking important aspects into consideration.