Well - I'd certainly take the advice from an experience guide and professional over mine. I'm still a kayak noob - but got into it cheaply to see how I'd like it. didn't wanna sink $2-3K into a unit and find out it wasn't for me. Plus I wanted 'extremely portable' (aka - lightweight) for where I was using it. (lotsa ponds I go to you have to portage it in - so the longer, heavier units ruled that out too. Mine are both in the mid 40's weightwise and both are 10 foot - but so far (with admittedly low number of trips and non on a stream yet) so limited experience there and never in bad weather. I can certainly see the advantage of a SOT (my next purchase) as both of mine are SINKs - but I'm 58 and would envision having to use a light trailer to transport. That's fine - but don't plan to get rid of my cheap lightweight ones at all. I got my Aruba 10 for $150 brand new - Have no idea if it's roto-molded or vacuum formed or what any of that even means. (so - Froggywaters - I'd love to hear more about that and why one is a risk for separation? ) I always wear a PFD - regardless of temp or inconvience - and at some point - I need to practice a deep water 'wet exit' to get familiar with how to handle that event. Don't care of I lose my 'gear' as I don't take much and never any of my better equipment.

I still have my 18' Bass Boat - but really love the solitude of the smaller waters and the simplicity of chasing fish with the minimal equipment needed. Just really relaxing and a bit of fun exercise as well...

But - to answer your question - I'm probably never gonna consider less than 10 as that seems to be my minimum size - but would a 9 work? Probably - there's a lotta folks using down to 8' models - that just seems very small to me - but it's whatever you're comfortable with.

I would say (like I would tell someone shopping for a bow, or a gun or bicycle - about anything) - if you can - try out the model you're looking for and make a more informed decision. Hard to envision from inside a store...
Good luck