I have a 17 word seed phrase from a 10 year old Bitcoin-qt/core? acct, but don't know what tool to use to turn it into a wallet. I also wrote down the 17 letter associated private-key itself. It starts with "q" and has two commas and a space in it?? Is that valid? Obviously I am terrified to put the seed phrase into any ONLINE tool. I want to practice offline somehow to see if I even wrote it down properly. I tried looking thru the sourcecode: https://github.com/bitcoin/bitcoin to see there is a word-list.. No joy. One guy said Electrum, but it didn't help decipher the individual words, just kind of a 'put them all in', sink or swim endeavor.... Thanks!
I have a 17 word seed phrase ...
Usually BIP-39 seed-phrases are 12, 18 or 24 words long. You can often add some extra phrase of your own, but even so, 17 words seems wrong.
... from a 10 year old Bitcoin-qt/core? ...
Bitcoin-qt/core has never used seed-phrases.
Electrum was first released in late 2011 and used seed-phrases - it used a proprietary system that has since been superseded by the standard BIP-39 system for seed phrases.
I believe the business behind the blockchain.info website used to provide an account (they may have described it as a wallet) that has a 17-word recovery phrase. See How can I recover a blockchain.info wallet from a 17 word phrase? or Help please recovering a wallet from a 17 word mnemonic phrase and other info and https://blockchain.info/wallet/forgot-password
The accounts feature in Bitcoin core was dropped some years ago.
There was never a private key per account. I believe Bitcoin-qt's accounts were mainly a way of organising addresses. The current equivalent is labels.
When people write about accounts, I always suspect they mean an online custodial account rather then a normal wallet. Bitcoin was intended as digital cash that each person looks after themselves without the need for any trusted third party. Accounts are associated with giving your money to some trusted third-party business and hoping they look after it for you. Some businesses call their customer accounts "wallets", which I think is misleading, but that's just one man's opinion.
17 letter associated private-key itself. It starts with "q" and has two commas and a space in it?
I don't think that is how Bitcoin private-keys are normally encoded. There are several encodings but the most common is probably Wallet Interchange Format (WIF)
One guy said Electrum, but it didn't help decipher the individual words
The individual words of a BIP-39 seed phrase are not ever deciphered. They are not the result of enciphering some plaintext. The whole phrase is the input to a mathematical operation (not encryption, decryption, encipherment or decipherment) whose result is a number that can be used as a private-key. The words are not intended to be processed individually.
I think Electrum is a good candidate but the information you are feeding it is not what would be expected. You also need to make sure that you are using electrum in a way that is appropriate for a legacy seed-phrase rather than the current system it normally uses.
With the information you have so far, I don't see any way to recreate a bitcoin-qt wallet - the information isn't consistent with typical use of Bitcoin-qt of around 2011. I'd look for other information, files on disk, backups, emails, records of downloaded software, etc.