I just want to know if it is possible to prolong an erection with the help of workouts. Are there any specific exercises that can be done to help with this?
While the penis itself isn't a muscle that can be trained, but simply speaking just a sponge for blood, there are three muscles that are responsible for supporting ejaculation and maintaining an erection via compression of blood vessels.
Musculus retractor penis
And there you have it, pelvic floor exercises are an exercise you should try. These exercises are often used in prenatal exercises and to reduce incontinece, but you can use them too. The muscle serve a different function for women and various other functions for men. So don't be confused if you find a lot of information aimed at pregnant women or for older men.
I read about men that used these exercises and were very satisfied with the results.
While these exercises seem to make use of special devices, there are "body weight" style exercises too, that only aim on contracting the pelvic floor muscles.
You should also aim for a good overall fitness, using other exercises (cardio, resistance workouts, sports, …) and a healthy diet.
While there is no specific exercise that will do this general good aerobic conditioning will help. So, keep going to the gym and stay healthy and you should have long, happy sex for years to come.