Much like everyone else has stated; a dildo is nothing like the real thing. Not only is a dildo rigid, you don't allow yourself to relax your body, but instead trying to extend and reach to play with yourself.
I say just try the real thing. The WORST that can happen is you can't take him at first, but you have the toy readily available for the guy to use on you. You'll be in a relaxed position to take the toy and to open up. Then may be, JUST may be, he will transition you to the real thing.
But hey, if you're not a bottom, at least you tried! Be proud of your tophood!