As mentioned in the introduction of Mabinogi, skills typically thought of as class skills are open to everyone. If you prefer archery but want a few points in melee skills you can do that. If you want to be a primary melee fighter with a few points in spell casting and archery, you can do that. Powerful mages can still use bows, swords, and other weapons(cheap Mabinogi money) and skills. The professions are just as open.
Your only limitation is how many ability points you can earn, as ability points are how you increase the ranks of your skills. Ability points are earned as you level(mabinogi gold), and you get bonus ability points as you age. Both age and level eventually hit a plateau, where you are not leveling often and you stop getting bonus AP for aging. The answer to this, for the player who is really feeling that lack of AP, is rebirthing.
