The skater needs a certain amount of experience points (EXP) in order for the player to upgrade it. Each upgrade gives the skater a chance to upgrade the rarity, and the chances are the same used on the mint.
When the skater reaches level 5, you are able to upgrade it only to reset its age.
Chance of better rarity for Common/Rare/Epic Skaters:
- Rare: 10%
- Epic: 4%
- Legendary: 1%
Your skater has an age and it's incremented by one every day (related to the mint date / last upgrade date). It will earn less when it's older, so you need to upgrade to reset its age.
- Age from 0 to 13: distance is lowered by 0%
- Age from 14 to 20: distance is lowered by 50%
- Age from 21 to 27: distance is lowered by 75%
- Age of 28+: distance is lowered by 100%
If the skater's age is 28 or more, you will not be able to train without upgrading.