To be honest, vibrato doesn't have to come for ages. You don't need it for fast tunes and I've met the odd guy who didn't approve of it at all. (Ignored him mind). That being said, the basic thing with vibrato is to make sure the fiddle is supported without your left hand and only have one finger on the finger board at a time. Keep your finger where it is and move your hand up and down the neck. Don't try and move your finger tip. Start it slow and it'll speed up naturally with time. Make sure the movement is as regular as posible or you might end up gradually drifting up or down the neck as you vibrato.