The invention relates to the use of a protein source comprising whey and casein proteins for providing an age-tailored nutrition system to an infant which system comprises two infant formulas each appropriate to an infant of a different age and each comprising the protein source wherein the whey:casein ratio of each formula is chosen in the range from 100:0 to 40:60 and decreases according to the age of the infant and the protein content of each formula is chosen in the range from 1.5 to 3.0g protein/100 kcal and decreases according to the age of the infant.
