I will be 40 in November and am doing a full time PhD (upgrade in two weeks - yikes!).

Education is never a waste, is it? Also, you are doing it for intrinsic reasons, which will possibly make the whole thing more enjoyable than if you are doing it for rat-race reasons, like me.

I suppose the question will really be an economic one, but many places hand out fee waivers. I have a bursary (which took ages to get) which makes it easier financially. I think in the scheme of things, doing it when the children are young is good because of the flexibility it offers. That was a massive consideration for us - I have a 5 & 3 yr old and the thought of working pt plus working towards a PhD (now an absolute necessity for Uni jobs where it wasn't before) killed me. I was working as an academic before, though.

If you want to do it and can manage it in your life, why not? Age is not really a big question given that you don't need it to do something for you in your career by a certain date, do you?

Plenty of PhD students in their 40s in my gaff. I would say yes.

I've just started my PhD aged 52 - I'm a mum with two teenagers, two dogs and a partner who's also a very busy academic high up in management, so life is a little crazy. I've also chosen to do it at a university 150 miles from where we live. It's not easy and I'm feeling a bit lost but I'm determined to succeed. I'd say go for it, you're a youngster compared to me.

If it will make you fulfilled and you can manage it then do it.

If you want to do a PhD for its own sake then that is the best motivation.

Are you planning on continuing with work during your studies? A p/t job alongside a p/t PhD with a young child wil be tough. You may find that family and work duties take over your PhD research time and what is already a long project p/t becomes untenable. The most difficult thing about a p/t PhD is to keep at it when you get distracted by other things. Practically you lose a lot of work when you are diverted from your research as you forget what you had read, your notes no longer make sense, etc. You need enough time to attack the PhD in meaningful chunks, I.e. enough time to read, digest and understand materials so that you can be inspired to write a chapter before you take a break. If you pause for a couple of months mid-chapter it's very difficult to pick up again.

You are not too old. You are amazing and great example as a Mum.
In my PhD cohort most of us were 35+, one lady was 82 when she started....and That's not too old either :)

You are definitely not mad :) I decided to change careers a couple of years ago and hoping to start a PHD next year (if I'm lucky and get accepted!). I had a lot of anxiety that this is something rather unusual... it turns out it is actually way more common than you think. I've met so many people over the past two years from all walks of life who are doing PHDs or changing careers in general in their 40s and 50s. We know ourselves better, we know what would make us happy and we do it:) Good luck!!

I'm older than you by a good decade and a full-timer PhDer. Our child was approx eight when I started. Having a kid makes work days shorter; you need to be fierce about your time and not scared to work at night. Looking back on my first two years, I see how much time I frittered.

You'e not mad, though. It's a rollercoaster at points, but a fantastic ride all the same.

My question would be if it's for personal fulfilment, why now when, with the best will in the world, it will be complicated? Maybe have it on the back burner as a retirement project or for when the baby is bigger?

I'm 40, doing PT work (of course it never really is) and a PT PhD with small DC and it's a complete struggle tbh. Constant guilt on every front.
If you can do it full time and have child care in place then I can imagine that would be easier.
I don't think your age matters at all though. It's all about the other demands on your time. Also I am doing this because I need to career wise, otherwise would not choose to do it now, which may also make a difference.

I'm 44 this year and finish my PhD this summer. I thought I would be the oldest in the research training sessions but I'm not by far. Be prepared for lots of bright young things who are able to grasp every opportunity though I'm not bitter.
I have loved the experience but it has been the hardest thing I have ever done and I'm not finished yet. I think it's been great for me though, challenging my brain when I could have plodded on in my previous job with much less mental challenge.