Rust 1.0 was in May 2015, it's only 6.5 years old, not 11 years.
The equivalent comparison would be where Go was in 2015, and I don't think Rust is doing poorly compared to that benchmark.
Anyway, Rust is seriously being considered for inclusion in the Linux kernel. I'd hardly call that a failed language.
For the purpose of maturity, the point in time by which to begin measuring the age of a language is the first point at which a stable release appears for general availability. Go is 9 years old, and Rust is 6.
If we're going by design inception dates, Go goes back to 2007 or earlier.
Not necessarily the troll's motivation, but: there's also a lot of "Rust envy"[1] going around from some people (mostly disgruntled C++ devs who feel threatened by it) who'll baselesly say anything and misrepresent something to prove their point. How does it never cross their mind that they're on the wrong side of things if they have to grasp for lies to prove their points?
[1]: I came up with the term just now, but I'm not sure "envy" is the right word; maybe "petty spite" is a better term.
The kernel is a crucible. I'm curious to see if it's system facilities are adequate and operate with reasonable costs in that context. We'll have to see, but I am still suspicious of what often comes across as hype.