Hi Laura, I am doing my PhD at the moment with an 18 month old. I have a really supportive DH though and couldnt do it without him. Uni definitely takes up time and you need to be quite organised and realistic to make sure everything with the kids gets done as well. But it can be done.
If it something you have always wanted to do then you will regret not doing it. As for the age, I don't think that matters at all. All the other things you have done in your life will add to your learning and teaching and will come out in ways you won't expect. Good luck with it!