YES. YES. YES.
That being said, if it's a first time, be gentle and don't go full steam ahead on him. I'd suggest starting with a blow job and the slip of a well lubed finger. If he likes it, add a second.
Don't let him cum though, you need to move on to tonguing his ass. The first time Violet did it, I could fully tell that she had pleased as many women with that tongue as she has. Holy FUCK. Get in there and show him a good time. But don't abandon the cock. Use a hand to stroke away.
Then move back to the fingers, or perhaps a plug and get on top of him while he rides out the sensations. As you're fucking him, ask him how good it feels, and how good it would feel if you had him bent over the bed, stroking his cock while you fucked him.
As he comes, REALLY, REALLY HARD (like, animalistic HARD here, not even kidding) let him know how badly you want to do it all again, and to elevate it next time.
Assuming it all went well, he won't be saving that ass for special occasions anymore.
Oh, and have fun! It might be butt stuff, but it's still just sex. Get on it!