They currently have the same 13 games. Six points with the remaining games of the season, there will still be plenty of opportunities.
Six points look big but it is small enough during a long season. 25 more matches will be enough for other clubs to catch Napoli.
Indeed, that is not too far a distance if you look at the remaining matches in Serie A, but the problem is that Napoli have not shown a decline in performance which will make the distance of points thin. They always make the most of the games they play, and in performance they are stable and don't appear to have any problems that would make their game not good. One by one the opponents that confronted them they succeeded in defeating. If other teams can not improve performance, then Napoli will move comfortably. And in fact the current rival team does not look ready to tackle Napoli.
The remaining 25 games will still be a World Cup. Napoli and Milan will probably still make a lot of mistakes. It's overconfident to say Napoli will definitely be champions this season. Remember besides that there is still a transfer market. If Milan or any other club has a lot of money I think Serie A will be even more interesting. Until now, they have never lost, they look convincing. Let's see until the end of the season.
At the moment, from the rankings, AC Milan are the most possible competitor with Napoli but it can change if Napololi lose 2 matches. Even Napoli have good form but losing two matches is not impossible. If they lose like that, it will give chances to other clubs under AC Milan to join the Scudetto competition.
Yes it is still too early to say Napoli will be champions this season with 25 games remaining. But it depends on their rivals who will still meet each other, especially in the second round of Serie A. The chances of Napoli going down are still very high, but will Napoli just let that happen? certainly not. They are the most perfect team now with no defeats in the league, it's hard to stop them.