If he's good enough, he's old enough.
Two months ago I would have said that it's too early and he'd better wait a year, but he's made such a big impression in the spring that my opinion has changed. Based on what we've seen in the past two months, he looks like a podium contender.
Of course there is a chance that this goes wrong. The expectations in the French media of the "next French Tour winner" can be a curse. If he has a bad day he will suddenly gets lots of negative criticism and have some explaining to do. On the other hand a 25-year old can also have a bad day.
His capacities over three weeks are an open question, but I don't expect him to collapse. Finishing between second and fifth in Paris seems realistic at this point, so it's probably the right decision.