How do you return a value when there are if-statements [closed]

In C#, I want to make a function regarding DateTime trying to calculate relative time from scratch and what I made was this:

using System;

public class Program {
    public static string getRelativeTime(DateTime past) {
        DateTime now = DateTime.Today;
        string rt = "";
        int time;
        if (past.Second >= now.Second) {
            if (past.Second - now.Second == 1) {
                rt = "second ago";
            }
            rt = "seconds ago";
            time = past.Second - now.Second;
        } // Then this process repeats until we hit years
        string statement = time + "";
        return statement + rt;
    }
    public static void Main() {
        DateTime before = new DateTime(1995, 8, 24);
        string date = getRelativeTime(before);
        Console.WriteLine("Windows 95 was {0}.", date);
    }
}

The problem about this though is that we can't return the value since it has been encapsulated by if statements, which I don't know how to fix. Of course break won't work since it is not a switch statement or a loop.

The expected output should be like this:

Windows 95 was 25 years ago.

So the main problem is, how to return an appropriate value in a function while the main values are actually being changed in if-statements?