getting the old form back

long story short, personal health issues with a family member limited my training these last 10 months. still got in a long 75 miler saturday and wednesday was an hour but the rest of the week its been 30 minutes on the trainer ..a few months ago,i started up again with no distractions but managed only 2 intervals of 10 minutes. i use to do after a good warm up, 10 minutes in the 53x19. rest 4 minutes then do another 10 minutes in the 53x18. rest 4 minutes. another 10 minute interval in the 53x17 . rest 4 minutes and then the last 10 minute interval in the 53x16. all at 100-110 rpms. done on my trainer..now i do the first two, and only get a minute or two into my 3rd interval. whats the best way, and training plan to do all 4 again? try and do an extra minute every week? 7-8 more weeks i'll have my 3rd interval done? then in 10 weeks my 4th done? or is there a better way? saturdays are a hard long ride and this interval workout on wed is my other hard ride of the week. the rest of the week i recover as i'm getting older and need more recovery rides..i'm a cat 2, but not racing anymore this year..only did a few in early spring. these last 10 months been tough, with limited training. how do i go about getting my wed nite ride back to completing the 4 ten minute intervals again? when i could do these a year ago, and with my hard 70-90 miler on saturday, i felt and did keep up with all the moves in the p 1-2 races. now , i'm 75% at best.hard to get the fitness back at my age..i really wanna try though. thanks