You're only 34 man, get out there and do it.
You don't want to get involved in any of this training nonsense, LEJOG
is the training, mental and physical, you get cycle fit as you go.

If you could do 40 miles on a canal towpath, you could manage more on a tarred road, say 50 or 60 miles, so that puts a 20 day LEJOG within your capabilities already.
You will have to decide about overnight stops..... tent, B&B, hostel, hotels, also how you will get to/from LE/JOG.
Just don't get saddled with a "friend" in a support vehicle like these TdF wimps, that just complicates the issue, more things to go wrong

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Oh and welcome to the forum from another eastcoaster

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