How long should I practice each day? 30 mins? 1 hour? 

The answer is how you should practice, not how long. Always have a practice plan for each practice session. It doesn't need to be complex. The main component is to state what you want to achieve or accomplish from the practice session. Some examples include: 

Play the left-hand part smoothly. 

Play rhythm of a song correctly. 

Practice scales and play them evenly. 

Practice both hands together evenly. 


In closing

You are never too old to learn how to play the piano. Your goal is to learn and have fun. Enjoy. The only person you need to impress is yourself.