Can my son have teething biscuits?

My son has only had rice cereal, but our doctor has given us the go ahead to move into fruits and veggies. He has no teeth, but I think he is teething since he is fussy and drooly and chomps down if I put my finger in his mouth. (clean, of course) He is 4 1/2 months old. Is he old enough for teething biscuits? How old was your child when you first gave them one? Do they help and did they like them?