Yes and no, respectively.
The yes refers to a few months spent in a suburb of Paris as a student. I soon realised that virtually none of the other students were buying tickets on the RER, as indeed many of the non-students, so I stopped too. They had inspectors who would come round but the trains were so crowded you had to be unlucky to get caught. I never was, but always felt guilty.
Far more recently, but still over a decade ago, I had the following conversation on a Bristol suburban train:
"One adult, one child to Stapleton Road, please."
"Is he under five?"
"Yes, he's almost seven."
"Let me try again. Is [nod] he [nod] under [nod] five?"
As you can imagine, an almost seven-year-old was outraged at being classed "under five"! We later (much later, he was 11) had a similar experience on the London Underground when I literally had no idea how to buy a child ticket; at that time (don't know about now) it was free up to 10 y.o. then a child fare till 16 (or 15 or 17 or something). Machines didn't sell such tickets, there was a window but closed, this was before tapping, but there were staff hanging around who said "He's ten, he goes free."