I'm probably in the same boat as you although I am younger than 30 
Not as lucky with injuries though, have had to endure two frustrating injuries (and before that a suspension) that meant I couldn't get close to playing any senior championship football in the last 3 years. I last played a league match about a fortnight ago, prior to that I hadn't trained in roughly 5/6 weeks due to injury that ruled me out of this years championship and which I played with for our last game. Suffice to say I was in some pain in the days after that match, even though I was still injured I never felt as unfit in my life.
What I did around October/November last year was join the gym. I made a point of going at least every other day, nothing serious weights-wise just a bit of everything to try and tone up a bit; complementing this with 5k runs at least once/twice a week, doing the same run each time and trying to reduce my time. Continued this up until and including pre-season (our club usually start late January), though I wasn't as fit as I'd have liked to have been.
This year I want to do the same though I think I will try it without the gym membership as I feel I have enough equipment at home to make use of. I would say 5k is more than enough to try and build your stamina, a rough guess I'd say I'd probably do it in 25 mins the shape I am in at the minute, I would hope to aim to reduce that by 5 mins before Christmas (ambitious enough).
The sprints is something I'm not sure about, I never did any sprint work at all last year but I'm sure it couldn't hurt to do a few, I always found the weather a bit of an obstacle with frost etc anytime I considered it. What our midfielders did this year after training was do 5 or so 3/4-pace runs from the halfway to the byline, not sprints but good exercises for the position they play. You could possibly do something similar to that on your own?
Not as lucky with injuries though, have had to endure two frustrating injuries (and before that a suspension) that meant I couldn't get close to playing any senior championship football in the last 3 years. I last played a league match about a fortnight ago, prior to that I hadn't trained in roughly 5/6 weeks due to injury that ruled me out of this years championship and which I played with for our last game. Suffice to say I was in some pain in the days after that match, even though I was still injured I never felt as unfit in my life.
What I did around October/November last year was join the gym. I made a point of going at least every other day, nothing serious weights-wise just a bit of everything to try and tone up a bit; complementing this with 5k runs at least once/twice a week, doing the same run each time and trying to reduce my time. Continued this up until and including pre-season (our club usually start late January), though I wasn't as fit as I'd have liked to have been.
This year I want to do the same though I think I will try it without the gym membership as I feel I have enough equipment at home to make use of. I would say 5k is more than enough to try and build your stamina, a rough guess I'd say I'd probably do it in 25 mins the shape I am in at the minute, I would hope to aim to reduce that by 5 mins before Christmas (ambitious enough).
The sprints is something I'm not sure about, I never did any sprint work at all last year but I'm sure it couldn't hurt to do a few, I always found the weather a bit of an obstacle with frost etc anytime I considered it. What our midfielders did this year after training was do 5 or so 3/4-pace runs from the halfway to the byline, not sprints but good exercises for the position they play. You could possibly do something similar to that on your own?
(I know I shouldn't - family ties)