Well, after 40 I think you're not really trying to grow anymore, so weight yourself weekly and adjust your eating to maintain a weight that's relatively healthy and you still look good. If you exaggerate a bit and put on some pounds, be strict until you're back in the zone.
Unless you compete or make a living out of bodybuilding. That's a different story.
I'm 50 and still growing. Albeit slow, as shit, but still gaining strength. I know the curve will fall the other direction soon. I feel it coming, but for now, I enjoy the slow ride up. I've switched to a more lean, vascular, GH look this past year and honestly I prefer it. So do the women. I can still eek out my sets of 315, 6-8 reps and I'm good with that. I just want to maintain and shred up and pop what I have now.