I do think it's fair to assume that if Hemsworth openly its likely to be possible more young kids will take it. But it also depends on how he talks about it.
Here's The Rock[1] at 48 years old. You can search for in-role Ryan Reynolds, Chris Hemsworth, Henry Cavill, etc, etc - Joe is tiny by comparison and all of these actors seem to get bigger and bigger as they age (look at any of them from roles 10 years ago) - which is the exact opposite of what happens to men as they age.
Here's an example[2] of what they look like (in "Hollywood" shape, but normal for age) when not tuned-up to the max on whatever they do/take for these roles.
[0] - https://www.essentiallysports.com/ufc-mma-news-unlike-the-li...
[1] - https://www.dailymail.co.uk/tvshowbiz/article-9166911/Dwayne...
[2] - https://www.popsugar.com/celebrity/photo-gallery/43926966/im...
On the getting bigger thing, muscle is cumulative as long as you keep exercising it. I have always assumed The Rock was on gear while wrestling (although he had a great frame to begin with) but I don't find it odd that he can maintain that at 48.