The age mainly affects its usefulness as an off-the-shelf guide to applied ML, because some of the currently best performing general-purpose algorithms aren't mentioned [1]. It also spends quite a bit of time on algorithms now considered mainly of historical interest, like version spaces.
So imo its main current usefulness is as a foundational text, which it's quite good for. It helps that it's also well written and understandable.
[1] A recent empirical analysis found that random forests and support vector machines seem to perform most consistently well at classification tasks, neither of which are in this book. http://jmlr.org/papers/v15/delgado14a.html