Elkington joins the Lambs from Toolstation Western League Premier Division side Saltash United.
He captained Cornwall’s under-18 county squad and was originally on the books at Plymouth Argyle.
He joined the Ashes in December 2020 after trialling with Luton Town.
Henderson said: "A number of clubs were in for Charlie and I am thrilled he chose to come to Tavistock, and was excited with our future plans and ambitions.
“He is comfortable in possession and can step into midfield areas. He is an intelligent footballer who is great at reading and anticipating a situation advance. I really think Charlie will fit into the group well. He is another young dynamic player who I am hoping will serve our club for many years.
"The fact Charlie only lives 5 minutes down the road from the ground, the Lambs can really sing `he's one of our own`!"
Koita returns to Tavistock from league rivals Willand Rovers.
The 19-year-old had made the reverse journey in October 2022.
He was quickly signed by Tavi manager Stuart Henderson from South West Peninsula League Premier Division East side Crediton United after an eye-catching display in a 4-4 friendly draw with Plymouth Parkway in September 2021.
He was the Crediton’s leading goalscorer before taking up the offer from Tavistock.
Tall, athletic and quick, he has all the attributes required of a striker.
Henderson said: "I am really happy Dan has chosen to come back to Tavistock. He is one of those players who I believe if everything clicked into place for him, he could play at a higher level.
“He needs to work hard on various aspects of his game to be the best version of himself, and I know my coaching team and myself will enjoy the opportunity to help Dan achieve this.
“He is a great athlete with a strong physical presence. Dan has decided to bring his pre-season forward as he wants to hit the ground running when we report back next month, and this just shows his commitment and desire to do great things at Tavistock.”
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