#but the reason most wizards are depicted as elderly is because wizardry is extremely difficult and takes a long time to master

[red-dragon-archfiend]

I don't have enough time or experienced with enough classes to write a detailed multiclassing guide, but for D&D players, especially new players, wondering if they should multiclass, the simple answer is "probably not". Multiclassing is, in general, bad. The game was not balanced with it in mind, and it's very easy to muck up your character if you don't know what you're doing. I'm not just talking from an optimization perspective, either; it's difficult to justify it narratively in a way that doesn't cheapen the significance of what class levels represent. You don't become a Bard by practicing the lute for a week. You can't become a Wizard without years of study. If you plan to multiclass, my advice would be to find some way of tying it narratively into your primary class somehow; an Eldritch Knight becoming a Wizard is sensible, because they already have an understanding of how to work arcane magic, they just need to spend some time focusing on that over improving their martial abilities to learn enough to start filling out a spellbook. Of course, that still takes a long time, but the Eldritch Knight's previous experiences mean they already know how to cast multiple spells already. If you want to multiclass for story reasons, ask yourself two questions: Is multiclassing really the best way to convey this change in my character, and, if so, do they have the adequate time, experiences, and resources to practice the skills necessary (physical training, study, spiritual attunement, etc.) to even START being that class? The reason I put so much weight into class levels is because the Player's Handbook itself makes a point to clarify what sets a member of each class apart from others who seem similar on the surface; not every soldier in a given army is a Fighter, chances are most of them aren't. And Paladins are even rarer! To achieve even one class level is a strong indication of skill and effort, and I as your DM would expect you to consider how your character achieves levels in a second class. My campaign features a Fighter/Warlock multiclass, and her patron is both the supplier of her occult magic, and her instructor, personally training her in her dreams, so she can level up in either class and it'll make sense. My favorite combination, Paladin/Sorcerer, can be explained by latent powers emerging in response to their experiences and the holy power they channel within themselves, perhaps a gift from their deity or the result of them or their ancestor slaying a creature like a dragon or vampire whose blood imbued the Paladin's bloodline with arcane magic. Maybe a Monk/Cleric comes from a monastery that reveres a specific deity, and that Monk caught their deity's attention, choosing the Monk for a holy mission. If multiclassing is part of your character's backstory or projected future, having a plan for it is key to making them still feel like a cohesive, singular character.