I tell you what , you run faithfully 4 times per week ......5km each time . Jog slowly. I shall garantee you that in a few weeks time, you be much slimmer.
Slowly, put in a lot of static exercise in your routine after the 5km run. The exercises are as follow :
Spider pumping
Normal Pumping
Star pumping
Burpes
Cruntches
I went reservist training during my 20s, they will ask the people to run 4km as warm up. Then do static exercise. Sometimes, they will in coporate sprinting to build up different part of muscle.
Go for a swim weekly to do some cross training , for let say 20 laps a time. You put in this concentrated effort for 6 months. You will be as fit as a PTI ... hahahah !!! Do it slowly, push a little if you may have to. The reason is to burn as much fat as possible. You need to keep it going as you age, your metablolism tend to slow down QUITE a bit. To maintain, you must be consistent in your exercise.
For oldies like me , i am trying to do it slowly. I cannot do it fast ... Sometimes i see the Gurkhas running in the evening. I can only match their speed for around 500 metre or even less. For me , if i sweat it considered exercising.