Your character has lots of skills, but none of them are useful where you are
A forty-two year old woman who spent her life being a French (or dark elf, mind flayer, etc) chef may have extensive knowledge of specific cuisines, techniques for cooking, and problem-solving skills tailored for a specific environment, but she can easily not know anything about riding a horse, sword fighting, or dungeon delving.
If you rolled a character like this, her skills and time spent as a master chef can translate into some overlapping skills. She may have a good dexterity score because she’s used to doing things precisely and quickly. She might prefer using a mace to a sword because the weight feels more like a pot she is familiar with. She might have a higher charisma than most because she ran the kitchen, though it’s not as high as it could be since she is in a new situation.
Despite having a non-adventuring career, she could have some skills that do directly affect an adventurer. Maybe she rode horses a few times a year, giving her a decent to good ride check. Maybe she climbed for fun, allowing her to have a higher climb check and the ability to handle ropes and knots well. There are a lot of hobbies she could have performed for years for fun that let her be competent but not amazing at specific, helpful tasks.
As long as you discussed it with the GM, you may not even need to put any skills in your particular craft. A skill like finding ways to make normal food taste like brains to satisfy a mind flayer’s craving is possibly too specific for a GM to require you to put skill points into it or spend experience to have. You can talk on and on about what spices are best suited to simulate the taste of memories, and most people are not going to be able to argue with you. It’s a fun piece of fluff to make your character more fun and well-rounded as a person.
Why did she stop being a master chef and start adventuring? That’s up to you. This character can have a whole life of experience and skills that don’t matter to 99% of adventuring.
This can work with pretty much any profession that isn’t adventuring. A mechanic, computer technician, blacksmith, or hotel owner isn’t going to have many maxed-out skills applicable to adventuring, though they will have lots of life experience that is useful elsewhere. And as long as they have a thirst for adventure, it’s never too late to start.
Your character lived an extremely sheltered life
You’re thirty years old, you have a degree, you know more than nearly everyone you know, and you were voted the most intelligent person in the village.
One problem: you’re part of a sheltered, extremist cult that believes the world is flat (or round depending on where your campaign is), magic doesn’t exist, you can only go to heaven if you are in within fifty feet of an elf that likes you, and everyone who doesn’t agree with the knowledge of your village is unequivocally wrong. It was only after you left your village that you learned the world is nothing like you were told.
A character that grew up learning all the wrong things could have half a century of misinformation in their head, and it wouldn’t add up to anything more than a kooky story to most people. Your knowledge of combat could be horribly flawed because someone who didn’t know what they were actually doing taught you. Your knowledge of ancient and recent history doesn’t mean anything to anyone else because it’s all the scribblings of a madman’s fever dream.
Even tasks like lockpicking and smithing could be useless if the village used shoddily produced locks and outdated smithing techniques. Any skill a character should be fluent in could easily be reduced to what a level one character would know when encountering the real thing.
Rather than everything you know being wrong, your character could learn what things they learned incorrectly. They may think they know more about something than they do, forcing them to relearn it the right way. They may get some things or some aspects of it right without having the full wealth of skills the character thought they had.
As a former member of a sheltered village or cult, a character can have a robust, interesting story that amounts to almost nothing when it comes to helping him understand people or being an adventurer.
Your character had such a privileged upbringing, they don’t know how the real world works
Your character might think they know how the world works, but their privileged upbringing has limited their scope. Surrounded by yes men who always complimented you despite not doing the best job, you don’t know what true skill is.
For example, a level one fighter could have ten years of experience with a fencing teacher. However, his lessons never covered how to fight dirty or how to fight non-fencers. Thus, his low bonuses to attack can be due to his lack of knowledge of how to fight in non-honorable combat without strict rules, a rest between each point struck, and no riposte following a point scored.
A character like this could have a high charisma but lack good diplomacy skills because he’s always talking down to people. He could consider himself a well-versed rider, but he’s not used to riding for more than ten minutes without a break. He could know what his level three class ability will do, but the stress of a real situation makes him too shaky or winded to use it properly yet.
This gives the character a lot of room to grow and even humble themselves, slowly turning into the version of himself he already thinks he is or changing in other ways. Getting knocked out of an ivory tower to find out how truly novice you are is a painful, life-altering event. Sometimes it shapes people for the better, sometimes it shapes them for the worse. How it affects your character is up to you.