[{_id:"notImportant",array:[{name:"Peter",age:17},{name:"Carl",age:21},{name:"sdsdsd",age:56},{name:"Ben",age:15}]}]

db.collection.aggregate([{"$project":{"max":{"$arrayElemAt":["$array",{"$indexOfArray":["$array.age",{"$max":"$array.age"}]}]}}}])