Hard to give advices without knowing exactly how you train now.

Detail your current training.

I can assure you that if you train light you will lose strength which is very important to hold on to as you age and also very difficult to regain.

stop lifting heavy, just do a pump workout and take some test, you will look and feel much better and you wont hurt yourself

Now in regards to how I cycle my training and diet, this may seem unconventional, but I can assure you that very very few pros and big guys actually train intensely year around.  Or diet very strictly.   In a nutshell, this is the schedule I follow :

January - March PHASE 1
I follow a program that is a modified version of the one Phil Hernon charges $300 for.   I didn't pay for this.  I sort of developed/came into this on my own.  It is a very short training program that is designed to increase your strength, "open up" the tendons and ligaments you use for bodybuilding exercises, and reintroduce the body to performing resistance training in a set movement path.  The only difference between my version and Phils is the exercises.  For instance, he advocates dips  - I don't do dips.  Etc..

(read on and this phase will make more sense later)

My diet during this time has my protein increasing, carbs lowering and healthy fats staying the same.

April - October PHASE 2
A more common schedule.  Pretty much what everyone else follows.  More volume - 10-14 total sets depending on the intensity.  Reps are kept in the 10-12 range. 

I do not do any cardio in the gym.  Not saying that I don't do cardio which I do, but it is usually outside riding my bike all day on weekends, power walking on the beach - sounds beta but walking on sand is a hell of a lot harder than walking on the sidewalk or a treadmill, basket ball, etc.. 

The advantage to PHASE 1 is that the strength increases I have gotten during that time are more beneficial here once applied in the way of doing more sets and more reps.

My diet during this time has my protein increasing higher, my carbs leveling off to a moderate amount, and my healthy fats increasing.

November - December PHASE 3
This is actually a recovery/recuperation period.  I don't body build or weight train at all.  I stay active, very active in fact but in other ways.  For instance one year I did two months of Cross Fit.  (go ahead and laugh, but at least I learned what it was about and how it did and didn't work for me), another year (and this past year that makes twice) I went to TRX classes 4x a week.  Using the bands and body weight exercises.  One year I actually taught the PM boxing class at Golds Gym 4x a week.  The absolute best thing I ever did was a few years ago there was a class that combined power yoga and foam rolling.  Sounds like something a woman would do, but it was fucking intense and the positions on the foam roller were down right painful.  I would love to take this class again, but the instructor went up to Palm Beach and they never got a replacement.

Basically what PHASE 3 is for is to first of all give your body time off from the grind in the gym and recuperate the CNS as a whole and any minor injuries or sore points you have developed over the year.  But keeping yourself in an "active rest" type mod.   By staying active with a certain intensity, you won't lose any gains you made over the year in the first two phases and you surprise the body by making it work hard at new things and in new ways.  Incorporating movements that are not locked into a set path of movement like bodybuilding exercises are.

Since PHASE 3 normally turns out to be more aerobic in nature, my carbs go up, protein down, healthy fats stay about the same as in PHASE 2.

Now.... to retouch on PHASE 1 again....

When the above two months are over and you have stayed active, tried new things, pushed your body in new ways.... you start back over the next year in January - March again.  Just like above.  This is the time you reintroduce your body to resistant training in predetermined pathways again.  You become familiar with the exercises again and reestablish a stronger mind/muscle connection that you didn't have from the random activities you did the last two months.  You keep the reps around 6-8 and wake up the muscle memory a bit.  You build strength in the muscles, and check out the tendons and ligaments to make sure any sore spots have healed.  You don't really need to do a full blown work out during this time because after being away from the gym for two months, you will have an easy time catching up and surpassing where you were a year ago.  The first month is basically a reintroduction and catch up.  The last two are where you start really working on the strength increases that will carry over to PHASE 2 and make the volume training more effectively. 

That in a nutshell is how I cycle, train and diet.