You'll know when it's the right time. If he tries, it's ok to say you aren't ready. If he truly cares for you, he will respect that. If he changes his Tyne and threatens to break up if you don't, then chances are he will after the kiss anyway, so save it for when you are sure.
If you are scared to kiss him then don't kiss him. Don't let him or anyone pressure you into doing something you aren't ready to do, or are uncomfortable doing. If you don't want to kiss him, then hold hands and hug, find other ways to show him you love him...kissing isn't mandatory....boundaries are.:)
Start with a kiss on the cheek. If you kiss him at least on the cheek at least he knows he's not in danger of a break up or anything. After a while of just sticking it to the basics, you might gradually get used to showing him affection, then you could move on to kissing him lightly on the lips. You'll find yourself getting let and less uncomfortable about it and you can decide whether you want to go take it farther whenever you want:) Good luck!