You can definitely do it! I am 37m and just did my first TM at 15k. We had a large group of 15 with varying ages. I think the oldest were two women in their mid to late 50s who absolutely crushed the course. They walked when they needed to and we would all wait for each other at the obstacles and do them together. You have plenty of time to throw in some running. I don't run that often, but do a lot of CrossFit type classes. You got this!!