At just 16, Verstappen was announced as an F1 driver, joining Toro Rosso alongside Carlos Sainz for the 2015 campaign.
It meant Verstappen would break the record for youngest-ever F1 driver at just 17, two years younger than Jaime Alguersuari - who previously held the record - in 2009.
Verstappen would move up to Red Bull in 2016, taking his first victory on debut at the Spanish Grand Prix.
Since then, Verstappen has enjoyed a plethora of success, winning three world titles, 53 races and 97 podiums.
At the time, given his age and lack of single-seater experience, the decision to sign Verstappen was heavily criticised.
Speaking on the F1 Nation Podcast, Tost - who will leave F1 after this weekend’s race in Abu Dhabi - spoke about Verstappen and the decision to sign him.
“Then of course Max [Verstappen]. Max because of his unbelievable speed,” he said.
“When we brought him to Formula 1, I remember back some of your colleagues came to me and said you’re totally crazy, how can you take someone who doesn’t even have a driver’s licence?
“And I said, I don’t want to discuss this with you now, come in five years and then we can discuss it because then I got tired of defending our decision.
“This unbelievable natural speed, you could see, sometimes in Formula 3, I remember back at this wet race at the Norisring, I thought Max was driving on a dry line because he was two seconds faster than the rest.
“This reminded me also of when Michael Schumacher won the Formula 4 race at the Salzburg Ring in similar conditions and he was also two, three seconds faster than the rest.
“And then this is important for me, I want to see what a driver is doing in our car.”