There is no such thing as "late" when it comes to starting uni and there isn't even a "usual" age. Even among school leavers many will have taken a gap year (or two) and that's not to mention the number of mature students who started uni later for a variety of reasons at a wide range of ages. Plus, unlike school, in any given module you are not usually going to have just one group of people of all the same age, because you may have e.g. PG students taking the PG version of that which shares the UG lectures, upper year students taking a given module as an elective (within or outside of your department) plus as noted above a wide range of ages in any given cohort anyway.
I did a foundation year at one uni, then continued to first year there, then swapped to another uni and course, and so was likewise 20 when I started at the second uni. There was no essential distinction between me and any of the other freshers (or indeed, most undergraduates), since especially for the ages 18-22 more or less the students largely have similar life experiences and expectations from uni and approach things in the same way. The "actual" mature students who were in their 30s and above still did also sometimes fully engage with student life and integrate into things - the older students (i.e. older than 25 usually) that didn't chose not to because usually they already had their own friends and family etc so just saw uni as a job and the other students as their colleagues, so while they were friendly they didn't see the need to engage in all the social avenues offered as they had their own social life outside of the uni already.