Misunderstood

[Leanne]

At a very first glance you’re so fragile and frail
Who would of known your past holds such a tale -- would have
You walk with a cane and a hunched over back
Never do you get any slack -- the meter in this first stanza is quite good, it echoes the gallop of the horses that follow later in the poem, and this short line to finish holds promise of more to come

I heard your story in an odd place -- this line is short if you want to stick to the meter you set up in the first stanza. Perhaps "in a rather odd place"?
A glass room just off the track of a horse race -- and this line's a shade too long
When you spoke no one would speak -- too short again -- with rhyming couplets in particular, it's quite important to be consistent with your rhythms
I stood on a chair just to get a peek -- overall this stanza builds well on the first, with insights into what the old man enjoys, or at least where he spends his time now

The stories you told gave me the chills
Filling my arms with many little hills
I caught sight of your eyes glistening bright
You held back tears with all your might -- "all your might" is an empty, overused phrase, which is a shame because "bright" is not a difficult word to rhyme.

Just as you finished the race begun -- the grammar is wrong here -- it should be either "began" or "had begun"
Horses went off to the sound of a gun
Ignoring the horses my eyes remained on you
I know you could sense them since you looked at me too

I was aiming for imagery -- you really don't need to say this -- imagery should be a given with poetry, and it's a fairly meaningless word as it's just an umbrella term for a whole host of different poetic techniques.

You do build the character reasonably well, although it probably could have done with either another stanza or a few less filler phrases/words -- my suggestion would be the latter.

As I said, when you're using rhyming couplets in a standard form like this, it's really important to pay attention to the meter or the rhymes fall in the wrong places and the effect is lost. There are plenty of exercises to help with your meter in the Poetry Practice forum.