The max speed depends on the equitation level of your mount. The max speed generally starts at 110, and then increases by one for each equitation level. So for level 12, it would be around 122 max, and then for level 13 it’s 123. When you reach level 15, it unlocks a special ability that relates to mount speed, but before that it mostly reaches its max in the 120s. During a race, obviously, the speed can increase further because of buffs etc. Still, the mount’s max base speed – the one determined by mood and shown on the mount’s page – generally has a maximum and minimum that is shown on the mount page.
The range of possible mount speeds can be seen on the mount equitation page. Here is Wistful’s (he couldn’t do this event for the first week or so), for example:
You can see ‘mood’ on the right, and I’ve circled it in blue below:
That section tells you the range of possible values for ‘mood,’ and hence ‘speed,’ generally. Hence, the value in the 60s is a minimum, and 122 would be a maximum. However, this range will increase by one when it reaches the next equitation level (minimum value possible will rise by one, maximum value possible will also rise by one, etc. Hence, maximum speed isn’t always the same value, it changes as equitation level develops.
Hope this helps.