The best drivers are the ones who are naturally fast - and natural speed tends to present itself very, very quickly. It might be Verstappen's first season in open-wheel cars, but consider the implications of that: he's second in European Formula 3, a series the FIA rates as being equal to GP2 and Formula Renault 3.5.
As for age, Ocon is 17 and Verstappen is 16. Both have birthdays in September, so Ocon, at least, would be "old enough". Although I have always felt that the legal definition of when someone is an adult is a poor yardstick to use for when someone is considered old enough to handle Formula 1, since the legal definition only takes into account physiology across the population, rather than individual maturity - which is what will decide their ultimate success or failure.
Is that your final answer?
Two minutes with Google will tell you that Ocon is a) already a member of the Gravity programme, and b) open to moving to Formula 1 if an opportunity presents itself.