Yup, Jon Jones was the youngest UFC champion ever, and now it seems impossible for anyone to beat him. That was a mixture of incredible talent, physical abilities and the fact he was ready to fight very often. Looking at his record, he fought 7 times in a span of 4 months in 2008. That surely got him noticed by the UFC. The times were different back then, the competition was not as strong as it is today and I don't even think any current fighter would be allowed to have an official fights every week like he did at the beginning of his career.
The top 5 youngest UFC champs:
#1. Jon Jones, 23 years
#2. José Aldo, 24 years
#3. Josh Barnett, 24 years
#4. Carlos Newton, 24 years
#5. Frank Shamrock, 25 years
Topuria did everything right in his career and he didn't even broke to the top 10. But he has at least 5 years of peak abilities to reign.