http://www.babycenter.com/0_age-by-age-guide-to-feeding-y...
This is a good link.
Also check with the American Academy of Pediatrics:
http://www.aap.org/
Next: ask your Pediatrician.
It is not by age, but ALSO by the baby's developmental cues... if the baby still has his tongue-thrust reflex for example, he is not ready.
Most recommend waiting until 6 months old to start.
And you have to know which foods to introduce first... and per their age and allergies. NO honey for example.
Also, you still must nurse on-demand for the 1st year. Per our Pediatrician, breastmilk or Formula is a baby's PRIMARY source of nutrition... NOT solids and NOT other liquids. Feed/nurse on-demand, 24/7 and especially BEFORE solids... otherwise the baby will "wean" from breast/bottle. And the baby will be TOO full to nurse/drink from bottle, if given solids first.
I would really ask your Pediatrician, for a recommendation.
all the best,
Susan