I may only be 5'10", but I do sometimes practice with people a good deal smaller than me, so for all intents and purposes I am tall in such situations. I find the difference in height does matter, but it is not necessarily a disadvantage. I may not be an advantage either. It's just... different.
In any case, you won't know until you try, and especially such an introductory course like the one you're going to take is very good for finding out if Aikido is something for you. I personally don't think you'll have any difficulties though, but then again, what do I know?