Homebrewing - Beer, Mead, Wine, Cider

A friend of mine dumped me a bag of malts he had lying around for like five years. It’s a kit for a Klosterbier which was stored in a plastic bag sealed with a clip, sitting on a shelf in a typical household storage room, so neither totally dark nor in bright sunlight, and slightly below average room temperature.

I’m hesitant now to heat up water and waste energy, time, hop and maybe yeast on these malts because I’m skeptic about how many enzymes are left in there. Have you ever used grains that old? Maybe I should mix them with fresh stuff?