All light or white oil base paints start to turn yellow after a few years. The only way to avoid this is to use a 100% acrylic paint instead. Acrylic paint is way more color stable. Simply prime the existing oil base paint, fix anything needing repair then paint with a good acrylic.

For the most part the prior answer is true. I would like to add that sanding before priming is generally needed. One thing to keep in mind as you restore a home is the lead concern in houses built prior to 1978. you might wish to check the EPA website for their recommendations.