i've red that you can use black&white cards till 6 month but of course not only.
so even if your baby is 4 still will nicely react for those cards.
from 4 months baby starts seeing colours but still very contrastic
best way is to check how he or she react, does like it much or not yet or no longer
my daughter Mia is 3months and still she loves black&white but i already observed that she likes strong colors like red, blue, green...
by the way do you know where can i find printables cards black, white&red?