How to find the max value in a Swift object array?

You can simply map users array to array of user's age and the find max age:

class Usr {
    var age: Int

    init(_ age: Int) {
        self.age = age
    }
}

let users = [Usr(1), Usr(8), Usr(5)]

let maxAge = maxElement(users.map{$0.age}) // 8

Swift 3:

let users = [Usr(15), Usr(25), Usr(20)]
let max = users.map { $0.age }.max()

// max = 25

struct User {
    var age: Int
}

let users = [ User(age: 10), User(age: 20), User(age: 30)]
let oldestUser = users.max { $0.age < $1.age }
oldestUser?.age  // 30

Use max(by:) function

class Usr {
   var age: Int
   init(_ age: Int) {
       self.age = age
   }
}

let users = [Usr(3), Usr(8), Usr(6)]
if let userWithMaxAge : Usr = users.max(by: {$0.age < $1.age}){
    print(userWithMaxAge.age)
}

It will print 8