Waiting till 6 mths is best.. Even if they are showing interest in your food
Why weaning early can be risky
The Department of Health recommends exclusive breastfeeding for the first 6 months of your baby's life. This is because most babies aren't ready for solid food before then.
There are several reasons for this:
Digestion: Babies under 6 months can't make all the enzymes needed to digest a variety of foods. Their kidneys also might not be mature enough to cope with foods other than milk.
Coordination: Babies need to be able to hold their heads steady and swallow their food. Babies under six months won't have developed this posture and coordination.
If babies are introduced to solid foods too early, they may be at more risk of:
Respiratory illness, celiac disease and wheezing
Developing allergies
Being overweight - introducing solid foods early is associated with an increased percentage of body fat
Why six months is around the right time for weaning
By the time they are six months old, the stores of iron babies are born with are running out - they need to get new iron from food.
Babies also need to take more and more milk to meet their needs - solid food is more concentrated.
Coordination-wise, your baby is more likely to be ready, too:
His jaw and tongue will have developed enough to cope with eating and swallowing food - making weaning a lot less messy
The process of dealing with food helps a baby's mouth and tongue to develop - helping her get ready for talking
Plus, most babies will have begun to cut teeth.
http://www.bounty.com/weaning/when-to-wean