$5.$ We haven’t seen him for 4 years.  
→It is 4 years since we last saw him.

$6.$ It’s over a year since I last went to see them.  
→I haven’t been to see them for over a year.

$7.$ It’s more than ten years since I last played football.  
→ I haven’t played football for more than ten years.

Giải thích :
$5$   - Cấu trúc: "It is + khoảng thời gian + since + S + V quá khứ" 
 $6$  - Cấu trúc: "It’s + khoảng thời gian + since + S + V quá khứ" 
 $7$  - Cấu trúc: "It’s + khoảng thời gian + since + S + V quá khứ"