A person or animal is an adult when they have fully grown up and matured. Before you are an adult, you are a juvenile.
Something is ancient if it is from the distant past, or is very old. Most things that are described as ancient are from civilizations that have since fallen.
Something is antique if it is old, and people think it is worth collecting. Some antique things aren't worth very much, and people just like to collect them. But other things become more valuable the older they get, and some antique items can cost a lot of money to buy. Antique is often used to describe an old, expensive item, while vintage is often used to describe a less expensive old item, but the two words can be interchanged.
Someone is elderly if they are in their older age. Elderly is a politer way of saying old.
A juvenile is a creature that is older than a baby, but not grown up into an adult yet. Juvenile birds often look scruffy as they are losing their downy baby feathers and growing their adult plumage.
The larval stage of a creature's development is its earliest stage. Many insects have a larval stage, and the larvae can look very different to the adult of the same insect.
Something is mature if it has fully reached adulthood. A fruit or nut is said to be mature if it is fully ripe. Other foods like wine and cheese where you need to wait a long time for the flavor to change are said to be mature when they are ready to eat or drink.
Something is old if it has existed for a very long time. Something that is really, really old is called ancient. When people get old they get grey hair and wrinkles.
Retro is a style where things that were fashionable many years ago are back in fashion again. A retro style can be achieved by using actual old items, or by making new things that have an old look.
Something is vintage if it is old. Vintage is another word for antique.Old cars and clothing are generally described as vintage, if they are in good condition. Vintage things may or may not be valuable, depending on how many people want to own them and how rare they are.