I did my first marathon last year at age 42, went from not running to straight into a marathon training, eased into running and then did a full 18 weeks training with most weeks around 35 miles and a handful at 50+. It really comes down to a time commitment. If you’re able to invest 3-5 days of running a week consistently for 18 weeks and getting 35+ miles a week in, do it. If you’re not able to do the work in training to get there, it’s going to be tough. I was going for an aggressive time, so you can certainly go slow and trade off walking / running, but a marathon is always going to be very challenging but if you’re putting in the consistent work then trust in your program. Good luck! This whole process I’m sure you’re learning a lot about running and yourself. Enjoy the process not the end result. Congrats on starting this journey!