MYTH – To play tennis properly you must have the correct form.
TRUTH – There is no single correct form.
Every good player adapts so as to maximize their outcomes based on multiple variables such as physicality, timing, and judgement. Within the professional game you will see a wide range of acceptable technical ways to strike the ball. The one provisos is that the range of adaption needs to avoid injuries.
Experienced teaching professionals can aid their students in adapting individual technique taking into account limits to physicality, timing, and judgement.
Students may need to adjust one of these variables in order to achieve a particular technique. Sometimes this is not possible. I had a 5 foot 5 inch gentleman request lessons so he could develop a Milos Raonic (6 foot 5 inch) serve.
If you are over 55 years of age do not expect to have the same timing you had at 35 and one of the most under developed teaching areas is to improve student shot selection or judgement which for many adult club players can be a game changer.
In the end, build your game to maximize outcomes, use technique that fits within a range that ensure injury free play.