I'm one year younger than you (48) and ran 3:19:45 last Sunday on slightly more weekly mileage (80-85) so I would say its very possible!
In my case the improvments have come slow, about 5 minutes a year, but I have less of a running history than you have. A 10 minutes improvement might work for you.
I'm back in training for next years race and will boost mileage to the mid 90's by July. My goal is a sub 3:15 (I'll be 49 then). My race times have improved steadily each year (with increasing volume and longevity) and I think that will continue well into my 50's (so long as I continue to train hard).
We may be close to 50 but our goals are not that unreasonable for our age. You should meet some of the really old runners at my track club. We have several national age group champions in their 60's and 70's. Even at that age they often outright win local 5 and 10k races beating people half or a third their age.
My club also has a 46 year old runner that is on the US national ultra-running team (last year he ran for the US in Austria and the China this year; both events were world championship races, he finished in Austria 7th overall, 2nd American). He does marathons all the time just to stay in shape.
Last week he ran the Long Island marathon in under 2:45 and did Boston 3 weeks before that in 2:32. In a couple of years, when he's our age, he will still be running under 3 hours. Gives me hope and motivation to keep working hard.