24 is definitely NOT too old! As long as your fingers work and you have the desire to put some time and effort into it, and have patience. Do you have a teacher? Trying to teach yourself, I don't know.... there are people who are self-taught, but a good teacher makes such a difference. Besides them sharing their knowledge and tricks with you, you have sort of an accountability there. It's a really embarrassing feeling to me to walk into my lesson without being prepared. I actually surprise him because I over prepare. I practice SO much because I want to make him proud that I'm always further along than he expected.
I did take 7 years between ages 9 - 16, and was a pretty good player. But I really didn't practice much or put effort into it. After being away from it for 25 years, and getting a teacher that I could relate to, because we're BOTH adults, and paying for the lessons with my own paycheck, I've put a whole new level of intensity into it.
So I think an adult beginner can actually make more progress than a child. There are, of course, his other adult students who never practice. I don't get that at all. Lessons aren't cheap. Why waste your money?
Pop music isn't that complicated. I think you could probably play some stuff within a year or two, depending on your motivation and if the instrument becomes your passion. I hope it does. There's nothing quite like the feeling of mastering a piece that seemed so difficult when you first sat down to learn it. You'll surprise yourself with what you can achieve if you put the effort into it.