simple List with max item count and age out capability

Timed.cs

public class Timed<T>
{
	readonly DateTime _time;
	readonly T _item;

	public Timed(T item)
	{
		if (item == null) throw new ArgumentNullException("item");
		_item = item;
	}

	public T Item { get { return _item; } }
	public DateTime Time { get { return _time; } }

	public double AgeInMinutes()
	{
		return (DateTime.UtcNow - _time).TotalMinutes;
	}
}

TimedMaxItemList.cs

public class TimedMaxItemList<T>
{
	readonly List<Timed<T>> _list = new List<Timed<T>>();
	readonly int _timeoutMinutes;
	readonly int _maximumItems;
	readonly EqualityComparer<T> @default = EqualityComparer<T>.Default;

	public TimedMaxItemList(int minutesToTimeout, int maximumItems)
	{
		_timeoutMinutes = minutesToTimeout;
		_maximumItems = maximumItems;
	}

	public bool Contains(T item)
	{
		RemoveOldItems();

		for (int i = 0; i < _list.Count; i++)
		{
			if (@default.Equals(_list[i].Item, item)) return true;
		}
		return false;
	}

	public void Add(T item)
	{
		if (item == null) throw new ArgumentNullException("item");

		MakeSpace();
		_list.Add(new Timed<T>(item));
	}

	void RemoveOldItems()
	{
		_list.RemoveAll(x => x.AgeInMinutes() > _timeoutMinutes);
	}

	void MakeSpace()
	{
		if (_list.Count == _maximumItems)
		{
			_list.Remove(_list.OrderBy(x => x.Time).First());
		}
	}
}