Skills

Skills are a significant part of what defines a character and what they can do. If you want to fly a ship, use modules on that ship, mine, trade, and so much more, you'll need to have trained specific skills for that. Additionally, training skills improves your performance (your ships will fly faster, your guns will do more damage, you will pay lower taxes, and so on). Some skills affect multiple areas of the game, but most are specialised. This has two major effects:

• It doesn't take too much time to become proficient in one area of the game (say, flying missile frigates), as there is a finite number of skills which improve your performance in that particular area. This also means that young characters (who have not been playing for as long) can "catch up to" older characters in specific areas of the game.
  
• Conversely, it takes much more time to become proficient in many (or even all) areas of the game; training every skill in the game to the maximum level would take around two decades of continuous training. In other words, older characters will be proficient in more areas of the game when compared with younger characters.
  

Fortunately, skills are cumulative, and once you have invested time (skill points) into a skill you will never lose them (with one exception: if you're flying a Strategic Cruiser and your ship is destroyed, you will lose one skill level in one of the relevant subsystem skills). This means that you can continuously improve your character's proficiency in one or several areas of the game, depending on your goals.

There are around 400 different skills in EVE, and every character can potentially learn every skill (provided that they have an Omega clone; Alpha clone characters are limited in what skills they can train)