Back at school

Back at Uni and putting the time into reading and writing. Submitted my first assessment piece today and feeling more focussed on the end result rather than the process - a bit more strategic than usual. I want to keep my results up to match what I achieved last semester. Can I do a PhD? Not sure at this stage. It seems like such a long haul to go for another Masters degree then do a 3-4 year thesis on top of that. I'll be 48 by the time I finish school. Bloody hell!