The 18-year-old, derided by some as a 'pay driver', has made notable mistakes so far in 2017 and is off the pace of his experienced teammate Felipe Massa.
Bottas told Le Journal de Montreal: "It's never easy for a driver to come into F1, and in his case, it's even worse."
"He is only 18 years old and the cars are much more efficient. Let's say he did not choose the right year to make his debut," said the Finn, who was set to be Stroll's 2017 teammate until he was called up by Mercedes.
"It's never easy for a rookie to compete with the world's top drivers who have a lot of experience.
"So you have to give him time and have patience before making a judgment about him."
However, Bottas thinks that Stroll is with the right team to support his push to get up to speed in F1.
"I know the environment well at Williams," said the 27-year-old. "He is well supervised and the managers there are used to facilitating the work of young drivers. I've been there."
Stroll enters this weekend's Canadian Grand Prix still chasing his first point.