Some people think that the older the horses are, the harder they are to train but that is a complete myth. It all depends on the horse. I would definitely start with LOTS of ground work and Liberty but no whips or ropes for the first bit unless you feel like the horse NEEDS the help to listen. And lunging does not count as Liberty.
Age doesn’t matter just do what you would do to an 2 year old
Honestly, age doesn't matter when it comes to teaching horses new things. As long as you get her respect through groundwork (move her feet through lunging, backing, yielding hindquarters, etc) and break any bad habits before training her then you'll be setting yourselves up for success! Solve any problems beforehand.