While earlier it was understood that infants needed solids at an age as young as 2 and 3 months, it is now established that breast milk is really all that a baby needs at least for the first 6 months of life.
While there is no hard and fast rule, the general indicator to be followed is that whenever a child starts to show an interest in solid food, starts to grab at it and generally exhibits the capability of handling solids, he or she may be started on to solids.
It is a good idea to let the baby have a few tastes of solids when he or she starts displaying such an interest even if a parent of care giver is otherwise of the view that an infant cannot yet handle solids.
This way, the child gets used to tasting things other than milk and will be well prepared to accept new and unfamiliar tastes and textures, which will typically require some more effort in swallowing as well.
Sometimes starting solids earlier than 6 months may be indicated; if the child appears hungry even after a feed or if weight gain is insufficient. It may be adequate to supplement breast feeding with a bottle however if even this is not seem to resolve the issue, solids may be indicated as early as 3 or 4 months.
Some babies however seem perfectly content to subsist on mother’s milk for as long as a year and show no interest in anything else. Their weight gain may also be adequate enough that solids seem superfluous.
However there is an argument against leaving solids off till too late: if a baby has not started solids till 9 or 12 months of age, he or she may then have difficulty accepting solids.
When you do start solids, whether at 6 months, earlier or later it is important to supplement it with breast milk for as long as mother and infant are reasonably comfortable with the idea.
There are nutritional, immunity and digestive benefits in breast milk that cannot easily be replicated by anything else.
Breast feeding along with solids is good for the baby because breast milk contains enzymes which help in digesting the solids. Also breast fed babies have had the experience of different tastes and flavors, so will take to solids more easily.
So really there is no one age at which solids should be introduced; let your baby decide, just don’t leave it too late!