Geile is a versatile German adjective that can mean 'awesome', 'cool', 'great', or even 'hot' (in a more informal, exciting sense). It's a very common slang term in German, especially among younger people, and adds a strong, enthusiastic flavor to expressions.
In this song, Ben Zucker sings "Was für eine geile Zeit" (What an awesome time), using geile to express intense excitement and enjoyment about the present moment and shared experiences with friends. It perfectly captures the celebratory and energetic mood of the song.
The song opens on a room that has filled up again — "Wir sind wieder hier / Unter Freunden zusammen" (We are here again / together among friends) — and the first thing Zucker notices is the gap: "So viele Jahre sind vergangen" (So many years have passed). He does not spend the verse on what was missed. He measures the night instead: "Jeder Tag wie ein Jahr / Jede Nacht ein Abenteuer" (Every day like a year / every night an adventure).
The chorus is literally a toast — "Und ich sing' dieses Lied auf das Leben, auf uns" (And I sing this song to life, to us). Geil is everyday German slang: crude at the root, but in this sentence it only means brilliant, so "Was für eine geile Zeit" sits close to "what a time to be alive". The last verse refuses to let any of it turn nostalgic: "Denn unsre beste Zeit zusammen / Fängt grade erst an" (Because our best time together / is only just beginning), and "Ich werd' nichts verschwenden" (I won't waste anything).