A sixteen-year-old is not old enough to vote in an election.
Here, 'enough' is-

• A sixteen-year-old is not old enough to vote in an election.
- Here, 'enough' is- ঘ) Adverb.

- এই বাক্যে, "enough" শব্দটি adjective "old" কে modify করছে (answering "to what degree?") তাই এটি এখানে Adverb.
- "Enough" শব্দটি Adverb হিসেবে সাধারণত adjective/adverb -এর পরে বসে তাদেরকে modify করে।

• More examples:
- Surely no one would be foolish enough to lend him the money?
- It’s small enough to fit in your pocket.

• অন্যদিকে,
• Enough (pronoun)
- "a sufficient number, quantity, or amount" ইত্যাদি বোঝাতে সাধারণত 'have' verb এর পরে noun/pronoun হিসেবে ব্যবহৃত হয়।
- যেমন: I've had enough of this behaviour.

• Enough (adjective)
- as much as is necessary (যথেষ্ট) অর্থে noun/pronoun কে modify করতে তাদের পূর্বে adjective হিসেবে ব্যবহৃত হয়।
- যেমন: Do we have enough lettuce for a salad?

Source:
1. Cambridge Dictionary.
2. Merriam-Webster Dictionary.