I probably walk less than 30 minutes a day and that is just to get from a to b. im pretty sedentary. could this lead to weak legs? how long to build back up strength?

From decondition to condition takes patience and time. Etiology of leg weakness can be due to decondition or other causes such as overweight, musculoskeletal disorder, or neurogenic issue. On your legs for just 30 minutes a day, you're too sedentary. You know your problem so you should become more active. If it is too difficult to do exercise by yourself, go to gym or practice with your friend.