Bf has never given me oral

soo... my boyfriend of a year and a half has never given me oral before. Truthfully I've never been too interested in him going down on me till recently...

We've been intimate since the very early months of our relationship and I have given him oral before but I guess what I would like some advice on is how I can go about asking/telling him that I'm interested in this now ?

In the very beginning of our relationship I remember he told me that he's never given any girl oral before so I don't know how to bring this up casually cause I think he's nervous a little about it.