The problem is that it will grow, and unless you are planning on trading it in at the point when it no longer fits (which isn't a very nice thing to do to a pet) it will be uncomfortable in your tank. I only have a 55 and I tried to convince myself that I could have one but it's really unfair to the fish and when the become stressed the get sick easier anyway, which isn't fun for you. So while, it's really up to you, I bet there are a lot of other fish out there that will fit the constraints of your tank.
BTW I'm planning on getting a yellow assessor too, I think.