What are the age/height/weight requirements for riding in the front seat of a vehicle that has an SRS airbag?

I want to ride in the front seat of our two cars (well, mini van and car). We have a 2003 (or 2002 I don't remember) Lexus, and a (I don't know the year) Dodge Caravan Minivan. It's one of those ice blue ones that are so popular these days it seems. There's usually multiple in parking lots.|||If you have an owner's manual to the vehicle then check to see if it lists that. Otherwise all I know is my vehicle has an airbag warning on the visor that specifies no one under 12 can sit in the front seat with the airbag as to an age.