The tricky part isn't actually the age mix - it's overthinking it. People want to celebrate you, not perform in some choreographed generational harmony. What matters is good food, a relaxed setting, and enough going on that folks can find their own groove instead of everyone staring at each other.
Pick a venue and format that doesn't force interaction. A dinner at a restaurant works better than charades in your living room. A casual backyard or park setup where people can eat, drink, chat in small groups, and move around beats a sit-down banquet where the 60-year-old and the 24-year-old are trapped next to each other. If you want something more active, consider a walk-and-talk thing (hiking, gallery browsing, or even mini golf) where people naturally cluster based on pace and interest rather than by mandate. Music should be low-key background stuff, not something that demands everyone's attention or makes half the room cringe.
Skip activities that feel forced or require everyone to participate at once. No team games, no karaoke rotations, no thing where younger folks feel babied or older folks feel forgotten. Let conversation happen naturally. Most people across age gaps get along fine when they're not being asked to do trust falls together. Keep it about marking the occasion and being around people who matter to you, and the vibe sorts itself out.