Im the same age as you and also have occasional stress-induced urinary incontinence (SUI) when doing high impact exercises. My doc suggested Kegel exercises and changing my diet but neither helped. Pads worked OK for activities lasting < 1 hr but caused me irritation on long runs. I heard that some elite athletes just pee on themselves during races but I'd rather not, nor do I want to take medications to reduce urination frequency or undergo surgery (yet).
I investigated other options (see http://kidney.niddk.nih.gov/kudiseases/pubs/uiwomen/index.htm) and eventually settled on using a pessary to force the urethra shut while exercising. But rather than having a permanent device inserted, I just use a super size tampon or a couple smaller ones (or a wad of TP if thats all thats available). This actually works very well for me except urinating is much less convenient (have to remove/replace it in a relatively private setting). But I think its a worthwhile trade-off and port-a-johns are usually located at regular intervals along most marathon courses, so I carry a couple extra tampons in a plastic baggy in a small waist pack along with my gels and run worry-free.
Hope that helps. Good luck on your first marathon!