i ve run 1.51.0 off this (althaough im in my 20s)
Mon: 4km in 3.40-30 /km than 2-3x 60m sprint full rec
Thue: 2x4x600 with (90s and 8min rec) in 1.48.45
Wed: 30min 9 min/ mile
T: 4x4 min at 5.20 or 85% maxHr with 90s walk , than 3x 10s hill sprints
F: 3x4x300 with 75-90s and 6min around 47-44, last one all out
S: 30min 9min miling ( short walk breaks inckluded)
S: off
wu p 8min 6x 100 stride, w down 5 min or so
when races are neer change the two interval workouts to
half sets of usual and a set of 1-1.5x race distance with minimal rest all out
ex: 4x600 90s 1.48 than 12 min 3x300m 40sec rest average 41 sec
other sets i used 6x200 off 30min
2x400 one min rec (this afterthe 4x600 or forexample 5x300 in 47 or so)
IMO if you want to run 1.51 you should be able to run either 50 for 400 and 3.55 for 1500, or sub 3.50 and 51-51.5 ish for the 400m
my go to advice is simple include these ALL YEAR LONG
long intervals (10k-3k pace)
threshold run or reps (83-91% MHR)
shor itnervals for anaerobic stamina (200-300-400 long about 800 pace to a bit slower than mile pace)
and shor max sprints with full rec (3x60m with 5min)
and than taking easy day Super super easy
my example week is probaly 50-60 mins or so training per day 6 times a week, very time consuming
good luck