He's trying to kill us--could ruin him--worry about that later--grab your sister and go.
"Oh! Yeah, wizards don't do that. You probably want a big commercial caster office with a huge network and maybe you can work something out where they call up their big customers and have you de-age them and then you can get a translation spell and a scry for your sister and a call or summon depending."
"I'm going to want to figure out something longer-term at some point, once I find my sister, assuming I can't just teleport us back home. Which I will want to try, but this is completely unprecedented as far as I know."
"Yoooou don't look like a dragon. Also. Dragons aren't real where I come from."
"If the identifying characteristic is hair color I'm not sure why the word you picked in my language was dragon. Dragons are supposed to be usually-large reptiles that may or may not have wings or breathe fire."
"...Aha. Stories about dragons in my world usually don't involve shapeshifting."