Everyone should be the same level. I should be allowed to make characters that are level 8 from the get-go. Experience needs to be handed out equally so everyone can gain their levels at the same time, and rewarding different classes for achieving different amounts of experience is outrageous. Levels themselves are a terrible notion and need to abolished. These are but some of the complaints I've heard about levels in my tenure as a DM. Some of them ring more truly than others: I have played and enjoyed many rpgs that do away with the concept of levels altogether such as BRP (particularly its incarnation as CoC), Hârnmaster, 7th Sea, and Aftermath!) but that doesn't mean I can't appreciate why they're used as shorthand for advancement.
Levels are a fast and easy way to determine how powerful a character is, for one thing. It works as a rapid shorthand for understanding just where they stand in the scale of might and it obviates the need to track all manner of niggly little advancements that would otherwise not be tied to level. I actually prefer the Hârnmaster/Aftermath method of skill improvement over levels, but those games are a bitch to teach to anyone who doesn't have an advanced math degree and the patience of a particularly peaceful deity.
The most common issue that I actually run into in my games is level disparity. Because I have a tendency to run lethal games and because Danny has a tendency to constantly be recruiting new players, we have a high character turnover rate. New people join in on old games, or old people watch in horror as some manner of awful creature slaughters their character. Either way, it leaves a core party (composed of the original two adventurers in this case, Crispus and Oloz) that is hovering on the door of level 5 while new players must join in at level 1.
I hear you thinking: "Josh, that's mean and not really fair," but you must be new to this blog, because that's sort of my shtick. No, it is not fair in terms of what the newbie level 1 characters can stand up to in a fight. However, it is fair in a number of other ways, and I will endeavor to explain why. Starting at level 1 is an integral experience for any player of AD&D, especially if they're new. It's not just to punish them for not joining the game earlier (it does punish them for that, I know) or for dying (it punishes people for that as well). Though, there is some validity in preventing someone who died from rolling up a character that is equal level to the one they lost and granting them a commensurate amount of magical items and other little advancement perks.
The primary issue here is that starting at level 1 is not actually a penalty, but rather an opportunity. Every time a GM "helps" the players out by giving them some kind of bonus or little perk (of any kind), what they are actually doing is removing an opportunity for players to achieve that bonus or perk on their own. That's right, I said it. You think you're being helpful, but you are actually robbing your players of the entire purpose of the game. You are KILLING YOUR OWN GAME. Achieving things is the only reason to play, and when you grant achievements without work, you remove the game portion of the game and it becomes wish-fulfillment fantasy time, which is fine if that's what you want but please don't condescend to call it a roleplaying game.
You don't believe me about the opportunity presented by being level one. I can smell it on you. Don't worry, I'll try to convince that it is in fact an opportunity. As we've discussed before, most characters are ciphers at level one. The player is still figuring out how they want their character to behave in various situations, how their stats come together to make up their personality. That's fine! That's good! Encourage it. Being a cipher at level 1 is part of the experience. Between levels 1-5 your character learns most of the things they need to survive for the rest of their careers. The experiences they have during these levels forms a backstory—not just one that you made up and wrote down, but a living breathing backstory that is part of the character as surely as your own history is part of you.
Building a new character at a substantially higher level, let's say 8, robs the player of that backstory. They're forced to rely on written backstory or no story at all. Written backstory, as opposed to lived history, is dead weight that drags a character down. It is a straightjacket that gives an ugly sort of inertia to a character because you are afraid to contradict it, or because there are hooks there that must be fulfilled. Writing down a complex backstory is stuffing your character into a cannon and shooting him out: you're just tracking a trajectory, not discovering new things about anything. Sure, he may bump into some shit on the way, but that's not excitement, that's just disappointing.
There are things that a level 8 character would have access to that no newly created level 8 character can. I'm not talking about spells and magic, since the DM could fudge those things and grant them to you anyway. I'm talking about contacts, friends, shared history, organizational knoweldge, and influence. These things are all earned by play and are not tied in any way to level save that someone who is level 8 has surely accrued a lot of them. Where did this newly minted mover and shaker come from? Why does no one know who he is? If people do know who he is, why are you forcing the DM to juggle fake (as opposed to living) backstory with real lived history?
At the point where a party is high level enough that you would need to make a level 8 character to adventure with them, you'd be better served by having the rest of the party retire temporarily while your new batch of characters caught up. Don't think of it as forcing players to start at level 1, but rather at giving them the opportunity to have their characters learn and grow organically, which is always a more satisfying process than simply writing down how they act and then forcing yourself to stick to that script forever.