When I taught, I also taught quite a few "second chance" students - i.e. people coming to university in their 20s, 30s, 40, 50s, 60s, and sometimes, 70s to study for a degree.
In almost every case, there was a strong reason for undertaking this study - especially on top of other commitments.
Some hadn't had the chance to go to university at 17 or 18, and always felt that they had missed out; others wanted to apply for a promotion at work (a police officer hoping to make inspector for example), often in the public service.
Still, circumstances may have ensured that yet others may have had to study something 'practical': I taught a man in his 50s whose father had died shortly before he left school, and who had felt obliged as a consequence to study for an engineering degree (for reasons of employability), which he never much cared for, but who had never had the chance to study what he loved (the humanities). And others wish to learn something new, stretch their minds.
For my mum, it was a mix of a number of these reasons - but, if you are going to return to study as an adult (with other commitments) you do need to be motivated and to actually want to do this.
A supportive family (emotionally rather than financially) - or family environment - can also be of considerable help.