use of modal verb "could"

Hi, Please check the usage cases of the modal verb "could."

1. When I was ten years old. I could play tennis well.

2. For three years before entering college, I could play tennis well.   

3. Three years before becoming a ten-year-old, I could play tennis well. 

4. A year prior to today, I played tennis well. -- It seems the use of 'could play' here wrong or awkward at best.

Thank you, CalifJim. Would you say that only context would tell whether the modal verb use of 'could' is referring to the present or is referring to the past?

I could play tennis well -- could be interpreted as referring to a person's present state ability -- how he can play tennis well now; but, it could mean how he could play tennis well in the past if some part or parts preceding it or following it indicate that. Right?   

Anonymous wrote:

Hi, Please check the usage cases of the modal verb "could." 1. When I was ten years old. I could play tennis well. You had the general ability to play tennis well at the age of ten.  It is not clear from this sentence alone whether or not you still play tennis well. 2. For three years before entering college, I could play tennis well.   This sentence suggests to me that you did not have the general ability to play tennis well before or after the time period mentioned. 3. Three years before becoming a ten-year-old, I could play tennis well. This sentence sounds awkward and forced because a normal and much easier wording would be "I could play tennis well when I was seven." (for example) 4. A year prior to today, I played tennis well. -- It seems the use of 'could play' here wrong or awkward at best.  To me, this sentence suggests one specific instance of having played tennis well.  However, the broader context might alter that interpretation.