Motivation can be tough at any time in this sport. I'm 59. I haven't trained seriously or consistently in, honestly, 15 years. I'd like to say I have periods every year where I'm serious about my training, but that wouldn't really be true. I haven't had what I'd call a "good race" in probably 20 years. I stopped defining "good race" as a good time well before that and now "good race" for me would be going through it with decent strategy given my current fitness level and feeling like I was in race mode the whole way, as opposed to "being in a race".
But I still love every run I go on and I'm happy I can get out there. I'll usually have a few 3-4 week periods in a year where I'll get out most days and run a few miles. Sometimes I can string a few of those together - a year ago I had a 100+ day streak which really made me feel pretty good about my running. Outside those times I get out once a week or so, maybe 2-3 times if the mood is there and maybe a little less if I get busy with life.
Over the last 15-20 years I've been a lot more motivated when I have people to run with regularly. Don't need every day, just need a few friends who want to be steady and get out once or twice a week and I can piece together a week. That social time is important.
Mentally it's darn tough to be so slow now. I was never a super fast guy, I did okay and was happy for what I achieved. At my best I was barely a sub 3 marathoner, had some decent tri's. Training pace BITD, I was cranking out 6-6:30s for my daily runs. Even in my early-mid 40's I was still able to hang at 7:30 or so for daily mileage. These days I'm struggling to dip under 10:00 pace, mostly because I've been so inconsistent this year. I've been getting back into it a little lately and I know if I stick with it for a month I'll be back down in the mid 9's and if I can keep any momentum going I'll be right around 9:00-9:15 this winter. I just laugh at myself when I get back from a run and download my watch data and it says 10:05-10:20 for the miles.
Injuries have been an issue for a lot of people I run with but not too much for me. Little stuff pops up but I get through those things quickly. I did have to shut my 100 day streak down last winter because I tripped on a sidewalk crack and took a hard fall. But that's not breakdown injuries which seem to be more career enders.