Pretty much what FeatheredFeet said.
I bought two of my TWH's as coming 3 year olds.
The 14.3H fella in my avatar had his height by that time.
The 16.1H fella grew until he was around six years.
Along with quality of care while they are still in their formative years, genetics may also enter into how tall the horse will get.
Regarding uploading pics: I'm not sure if you have to make certain number of posts before you can upload??
They can either be uploaded to your album on Horse Forum then copied into your post.
Or loaded into Photobucket or some other on-line service, then click on the "insert image" square icon in the top bar and copy/paste the URL link
You may be able to post pics directly from a Smartphone but I don't have one, so don't know the process