If your window frames need repainting, you should consider linseed oil paint. It’s non-toxic, has no volatile organic compounds, and hardens by chemical reaction with the air. I first used linseed oil paint on wooden windows in 2008. They haven’t needed any maintenance since and they only need repainting now. There’s been no peeling, just a surface coating that’s weathered away.
You’ll get the best results if you first slake the thirst of the old wood by brushing on boiled linseed oil. I use a protein-free formulation (you can buy it and the paint online from Sage Restoration) because it doesn’t turn black when you use it outdoors, unlike the kind you get at the hardware store.
Linseed oil paint can stain exterior walls below your windows as rain washes the pigment downward. Apply two thin coats of paint after the boiled linseed oil to avoid runs, and let each coat dry for at least 24 hours. Over time, the coating will thin, and the bare wood starts to show through. Then it’s time to clean the cobwebs off and recoat again.