You can never be too old to get a doctorate. However, be aware that some things will be different at this age than they would have been if you were doing this when younger.
You will need to be able to hold large amounts of information in your brain (mainly citations of relevant papers) – this will not be as easy as it once was.
You will likely be less willing to take crap from your supervisor, or work for years on the very low salary offered by your supervisor or the department.
You will find it easier to wonder if the whole thing is really worth it. A PhD is a lot of work, more than you think it will be. Most people question their decision to do it at some point. As an older student, you actually know what you could be doing instead.
And unless you already have a job in your field, and are considering upgrading your credentials to make more money or aim for a specific type of position, your job prospects will probably not improve by getting the PhD. Do you have a financial plan in case your degree takes longer than the university will support you for?
I’m not trying to discourage you – I’m just saying that you should be aware what you’re getting into, and that you will be in a much better position to do it if you can support yourself during and after working on the degree.