Very variable depending on general lifestyle, level of education, job setup, friends etc.
Is it a case of her and her friends have decent jobs, living with partners, bought houses, checked off lots of milestones? What about her partner?
Or did she go to uni, only graduate a year or two ago, in an entry level job, living in a rented room in a HMO, still living a 'young and free' city lifestyle? What about her friends and partner?
What's the partner like, and how's their life together?
As someone who went to uni, at 23 I'd been graduated about a year, was still working a shitty job, living in a tiny rented 1-bed flat, still living a bit of a student lifestyle in terms of going out drinking, seeing friends with little notice. Most of my friends moved away for uni, and were living and working in similar situations at that age, for us getting engaged would have been unthinkable, and if we did we wouldn't have had the money to get married (and it's have been fair for parents to point that out).
My sister was engaged at about 23, she stayed with parents and worked full time at 18 rather than going to uni, and had worked a couple of decent jobs, had bought a house in a small town near my parents with her partner, and has several friends with very young children by 23, so her lifestyle fitted in with that.