It's not specifically about ab initio training but relates more to the rent or reward from the aircraft. You may not use an engine that is 10 years old + 20% for commercial purposes
can't remember where that is specifically
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If you own the plane and aren't actually gaining anything from the use of the plane then it's entirely possible that the CAA will allow you to train on an aircraft with an engine older than 10 years. Give them a call and ask.