Here is your answer – No. You’re never too old to learn anything, including a guitar. Applying yourself to learn an instrument has nothing to do with your age, but rather with how much time you have (or, rather allow) to practice. Not everyone will be Eddie Van Halen, but with proper instruction and time put in you can get playing.
Your boss at work, or your customers don’t care if you play the guitar, golf or like to fish. As an adult life brings more challenges, people feel they can’t really commit to playing. 20 minutes every 3rd day is not going to do it, even if you had the talent of Eddie. I have seen some of my younger students get incredibly good at a guitar in rather short period of time. Their advantage was having the focus and time to sit at the guitar and play it for 5 hours plus a day.
I started to play the guitar late, I think at 15-16. Most of my friends were much better than me. Ok, all of my friends were better than me. But, I have put an immense amount of practice during my High School years (Read: no time at the beach, no hanging out, no parties) and most of them were not even in the running by the beginning of my Junior year.
I also mentioned this before, but I never met anyone whose fingers were too short, too long, too stubby to play the guitar. That excuse does not exist.
So, how much time do you need to get some decent playing in? If you can dedicate honest 30-45 minutes 6 days a week, you would have made a great progress in 3 months. This will be enough to play several songs, melodies and most likely even write your own stuff. If playing an instrument is important to you, often times you have to give up on other things to find the time. For adults, it’s a game of priorities and time management and figuring out what’s important.
I also believe that we should all carve out at least 1 hour every day to do the stuff we love to do. It’s necessary. Otherwise, life becomes a boring box you live it.