private class Treshold
{
    public Treshold(TimeSpan value, string description, Func<TimeSpan, int> converter)
    {
        Value = value;
        Description = description;
        Converter = converter;
    }

    public TimeSpan Value { get; }
    public string Description { get; }
    public Func<TimeSpan, int> Converter { get; }
}

public static string RelativeDateTime(DateTime theDate) => FriendlyTimespan(DateTime.Now - theDate);

public static string FriendlyTimespan(TimeSpan t)
{
    var thresholds = new List<Treshold>
    {
        new Treshold(TimeSpan.FromMinutes(1), "{0} seconden", x => x.Seconds),
        new Treshold(TimeSpan.FromMinutes(2), "één minuut ", x => x.Minutes),
        new Treshold(TimeSpan.FromMinutes(45), "{0} minuten", x => x.Minutes),
        new Treshold(TimeSpan.FromMinutes(120), "één uur", x => x.Hours),
        new Treshold(TimeSpan.FromDays(1), "{0} uur", x => x.Hours),
        new Treshold(TimeSpan.FromDays(2), "gisteren", x => x.Days),
        new Treshold(TimeSpan.FromDays(30), "{0} dagen", x => x.Days),
        new Treshold(TimeSpan.FromDays(365), "{0} maanden", x => x.Days / 30),
        new Treshold(TimeSpan.MaxValue, "{0} jaar", x => x.Days / 365)
    };
    var threshold = thresholds.OrderBy(x => x.Value).FirstOrDefault(x => x.Value > t) ?? thresholds.Last();
    return string.Format(threshold.Description, threshold.Converter(t));
}