If your goal is size it should be obvious but make sure you are eating more than you are now. Doesn’t mean eat tons more or eat a bunch of junk. Just make sure you are putting in extra calories and nutrients your body can use to build new tissue. Lots of people work out hard and then starve themselves and wonder why they don’t get anywhere.
If you work out and are growing in the right manner your scale weight should be increasing and your lifts should be getting better (ie. More weight on bar or more reps for a given weight).
At 40, do yourself a favor and forget about “bulking”. Just eat a bit more than before and monitor what is happening.