just find a first year calculus book. In general first year calculus ( as well as physics/chemistry) books are very accessible and good for self study. Make sure you study the ~70% percent of the end of chapter problems with answers. In fact, I got the top letter grade in the calculus course...
I am a Ph.D student and I have it all. If you don't do socializing/exercising, it is very probable that you will be burnt out in the graduate school. You don't want this because when you are burn out, you can't get things done, you are not efficient at all. So, having a balanced work/social life...
I don't think that it is hopeless at all. I know a friend who just started his M.Sc. degree at the age of 29. However, since you don't have a physics background, you might need to take many undergrad courses. I strongly suggest that you send e-mails to (many) graduate study coordinators at...
24 years is neither an early nor a late age to start Ph.D. in physics. I am a Ph.D student and by the time I graduate i will be of age 30. Also, I know other graduate students in my department, and they will be of age 31 by the time that they finish their Ph.D/M.Sc degree in physics. So, go...