Whoever told you he was slow doesn’t know anything.
Most players see a deterioration in their skating as they get older and that’s the prime thing that causes their game to decline. In Nash’s case, he kept his skating, but his reaction time and quick-fire neurons are what deteriorated. Because of that, he can’t always get a deceptive shot off, which was the heart of his goal scoring. That goal he scored tonight? That’s an example of what he can’t do anymore on the regular. That strange quick shot that surprises the goalie. It’ll still happen on occasion, but not often enough to score 35 in a season anymore.