My 5 month (and 7 days) old LO has been rejecting milk especially when he sees us eat. Usually drinks 160 ml but will only drink 30 ml in the evening the last 3 days... is it because he sees our food and wants to eat? He's been wanting to grab our food and salivating a lot. Should we start with purée food earlier?

Yes u can start giving baby solids alrdy. As long as baby is able to somewhat sit up right. I also started my boy at 5+ months because his milk intake drop. U can go for cereal or purées that u will add his regular milk to it so that it is a familiar taste still and helps hit his min 600ml milk intake a day

Sounds like your baby is ready to try solids soon since he is trying to grab your food. Babies go through periods of rejecting milk and they will bounce back again so I won't be too worried. Perhaps you can try giving him cereal already?