Cool thanks
Ok my work out is like 4 days a wk. & about 1to1/12 hours. I do the basics mostly free weights. Abs, lats, delts,curls, flys,pull ups, push ups,ride some miles on the bike.
Some of the posters hit on diet, so I will take a few other routes too...
Keep in mind it takes time to build bigger mass, especially in the large groups ie: legs, glutes, back, shoulders and chest especially. I know some guys say they do not care about those areas, but the truth is, these are the large muscle groups that make the difference in carrying more bodyweight and put your body into a hormonal situation to grow some. Working the smaller groups, as you mentioned, are okay too, but to get the most out of mass training, IMO, you have to train the largest mass of the body with a good solid 5-7 compound exercise routine.
#5-#10 pound gains in lean muscle in a year is pretty great. If it does not sound like much, look at #7 pounds of hamburger on a plate.
And no, I am not a younger guy than you talking about gains for a 40 yo. I am 55 and still hit it hard. But as I said, it takes time, so make it a life long habit, don't rush or try short cuts and you will be better for it.
All the best