I read somewhere that as older a bitcoin become as higher exchange fees the buyer has to pay. Is that correct? These exchange fees go to the miners only or to whom else?
thank you
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No, the transaction fee is not increasing over time. According to the Bitcoin wiki, these are the rules under which the reference implementation decides weather or not to include transactions (and therefore how fast they are confirmed):
27.000 bytes in the block are set aside for the highest-priority transactions, regardless of transaction fee. Transactions are added highest-priority-first to this section of the block. Then transactions that pay a fee of at least 0.0001 BTC/kb are added to the block, highest-fee transactions first, until the block is not more than 250,000 bytes big. The remaining transactions remain in the miner's "memory pool", and may be included in later blocks if their priority or fee is large enough.
The priority addressed in the bold part is calculated like this:
priority = sum(input_value_in_base_units * input_age)/size_in_bytes
As you can see, the priority increases with the age of the coins. Thus, the "older a bitcoin gets"* the more likely it is that the transaction is included in a block, even if no fee is paid, in fact.
This behavior has the following advantage: That way you have the option to pay more fees to get your transaction confirmed faster, or less and even nothing if you can wait a day or two.
Regarding the second part of your question: Yes, when a miner generates a block he gets the transaction fee of each transaction in this block.
* to be exact: "the older the last transaction spending the coins is"
When buying bitcoins with fiat, exchange portals like MtGox or Bitstamp usually charge another fee (about 0.5% on both bitcoins and fiat), which does not go to a miner but to the exchange portal. It has nothing to do with Bitcoin fundamentally, so it's totally up to the exchange how to calculate this fee. However, I don't know of any exchange which considers the age of the bitcoins, and I can't see any reason why they should.
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Thank you. ONe last. Are the large portals like bitestamp that decide if to pay or not the fee or is the user? – Sean Black Dec 19 '13 at 7:31
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Rereading your question and your comment, I have a feeling that I didn't understand your question completely. The answer I wrote discusses transaction fees (which are paid when transfering bitcoins), not fees paid at exchange portals (when buying or selling bitcoins with fiat). I extended my answer. – jnnk Dec 19 '13 at 9:21
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The transaction fee is determined by the one who sends the bitcoins (this happens normally behind the scenes by the used wallet software, you may not be able to change the default behavior). The exchange fee is set by the exchange portal. – jnnk Dec 19 '13 at 9:27
