so many people do gap years, its more common than you think... you will meet people of all ages at uni 18-50s and possibly beyond that. Age really is not a big deal, as how it may feel having to resit a year in school. I went straight to uni at age 18 and found that the majority of people in my first year fit within the age bracket of 19-21, which made me one of the youngest.
I also did my first university placement with a lady who was 38 when i was 18! She was also in first year like me. So there you go even people who are almost 40 go to uni... we got on like a house on fire despite the 20 year age gap. You will meet people from all walks of life, ages and aspirations