I retrained at 39, OP.
I'm not yet 5 years into the profession and was thinking of taking a break come September. As it is, I'm hoping to continue in my current school, but I haven't the energy to apply for a new school.
What do I love about the job? I love working with the children - every day brings something new. It's also perfect for spending time with my own dc over the holidays. I work with a great department, and appreciate how lucky I am in that respect. It's not just the academic side (I love my subject), but also the pastoral side. Caring about, and being able to do something beneficial for children. We all want to leave school with a positive experience behind us.
What do I not like about the job? It has placed a real strain on my marriage - it has been a very tough few years and my dh has struggled to come to terms with the commitment that the job requires, and felt as if everything was controlled by how much work I had to do in the evenings and the weekend. He is a good sort and has taken on much more of the organisation and work at home, despite working very long hours himself.
I'm in school from 8am to 7.30pm most days, but this is to try and reduce the amount of work that comes home with me (I try not to work in the evenings). I'll typically spend 2-3 hours a day at the weekends preparing for the next week. It definitely means that I'm less available for my own dc during term time, which, tbh, is a rubbish feeling. We also have excellent childcare (nanny) which costs an arm and a leg, but she is worth every penny.
I also find it hard to switch off, so am always thinking ahead to the next day's work. My sleep is pretty poor nowadays, which I think will have long term effects on my health.