how old should you be to use this, can my 13 year old daughter is it?

I don't see why not; she's old enough to keep her eyes and mouth closed and hold her breath long enough to spray it on :-) She'd be wearing a full makeup application, I'd expect. Check out Patrick's primers, for oil and sweat control; I'd recommend them for when doing a full makeup application AND when just wearing sunscreen and powder, OR just one of those, OR even no "face" makeup :-) Also, re this spray & any areas of dry skin, check out the answer w. solve someone posted below (above?) :-)