Often Players that have been around awhile are reluctant to let their characters age at all as in the past 1 RL year was equal to 6 Yliakum years. As you can imagine, people would be killing off their characters a lot faster than they intended, especially if they played diaboli.
Some people would choose to age their character as the RP called for it. If you had a child character and you wanted to start to make a warrior out if it. You might just decide to start RPing them as a 20 years old and just not worry about all the time in between.
Some people choose to just periodically age their character by a year. How often that happens depends on the person.
Some people never age their character as the character's age plays an important part in how they RP them. For instance, an innocent child, a headstrong youth, a wise elder, etc...
A few things to consider:
If you are RPing with other characters and their characters aren't aging, it shouldn't become problematic to age your character until you age your character out of an entire age group (i.e. child, teenage, adult, etc..) That causes the RP dynamics to shift a bit and can cause some inconsistencies. However, if everyone is cool with the inconsistency then it's not really a problem.
For whatever reason, people typically skip the teenage years. So if you play a child character and then you put it on the shelf for awhile, only to bring it back as an adult, I don't think anyone will mind much.
Currently time in Yliakum is more like the passage of real time. Their days correspond to ours so aging is slower now and should be less of a problem.