reif
ripe
Fully developed and suitable for eating, usually referring to fruit or vegetables.
Diese Bananen sind schon sehr reif, du solltest sie bald essen.
These bananas are already very ripe; you should eat them soon.

ripe / mature
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ripe
Fully developed and suitable for eating, usually referring to fruit or vegetables.
Diese Bananen sind schon sehr reif, du solltest sie bald essen.
These bananas are already very ripe; you should eat them soon.

You can recognize the meaning of 'reif' (ripe/mature) from context. If it refers to food, it means 'edible' or 'ready to eat'. If it refers to a person, it means 'mature in thinking'. If it appears with 'für', it means 'ready for' or 'urgently needing something'.
Die Äpfel sind reif, wir können sie pflücken.
The apples are ripe; we can pick them.
The construction 'reif für etwas sein' (to be ready for something) is a fixed expression that is often used colloquially to express that you urgently need something. A very well-known idiom is 'reif für die Insel sein' (to be ready for an island getaway / to badly need a vacation).
Nach dem ganzen Stress bin ich reif für die Insel.
After all that stress, I'm ready for an island getaway.
In the meaning 'suitable for eating', 'reif' (ripe) is typically combined with fruit, vegetables, or cheese. Examples are 'reife Bananen' (ripe bananas), 'reife Tomaten' (ripe tomatoes), or 'reifer Käse' (ripe/mature cheese).
Für das Rezept brauchst du sehr reife Tomaten.
For the recipe, you need very ripe tomatoes.
'Reif' (ready/mature) can also be used for abstract things like plans, ideas, or decisions. It then means that something has been fully thought through and is ready for the next step. A fixed expression for this is 'die Zeit ist reif' (the time is ripe).
Die Zeit ist reif für eine Veränderung.
The time is ripe for a change.
ready
'bereit' and 'reif' can both express that the right moment for something has come. 'bereit' usually refers to a person: someone is prepared or wants to do something. It can also show that someone agrees to something. 'reif' more often means that something is developed enough or that someone is in the right state for something. In fixed expressions like 'reif für Urlaub' (ready for a vacation), it often sounds as if you urgently need something. Learners may confuse the words because both have to do with 'now it can begin'. In practical terms: for a person's willingness and preparation, you usually use 'bereit'. For development, the right state, or 'urgently needing' something, 'reif' fits better.

Nach dem langen Arbeitstag bin ich wirklich reif für eine Pause.
After the long workday, I am really ready for a break.
Nach zwei Wochen Vorbereitung bin ich bereit für die Präsentation.
After two weeks of preparation, I am ready for the presentation.