I don't know how big 5.5ft is, but I'm around 165cm tall and about the same weight as you, And I've ridden my 38" miniature, but before I get ripped in to about being cruel to my animals, I only ride her at a walk, and only for 3-4 minutes before my sister gets on, and only if said miniature isn't in work, if she is I don't get on first but I would rather she threw me off rather than my 6yo sister.
The smallest horse I have ridden "properly" like walk, trot, canter etc, was 14.1hh and that was a few months ago and he is my best friend's pony.
My smallest actual horse, that I own is 15.2hh and I have just bought one who is 16.1hh.
So there's not really a limit on the size you can ride depending on what you do with them. I only rode the 14.1hh on the flat, I could have jumped him but he was sooooo lazy. I showjump my 15.2hh.
R.I.P ~ Bubbles - 25yo tb mare - 13.04.2011 ~ 8:30am ~ passed away naturally and peacefully in my arms
Last edited by HollyBubbles; 12-27-2010 at 06:46 PM.