I'm currently trying to gain at age 35, I eat until I can't eat another bite and lift hard 3 days a week. Gaining weight comes slowly.

Stuffing yourself with solid food is indeed a chore. Shakes are an easier way. As is dumping butter and olive oil in your carbs. 1 teaspoon is 100 calories.

Funny I was in the same boat for first 2 years of working out, starting bulking with more oils, butters and shakes in addition to my usual 1 cup of carbs per day. Gained plenty of fat. Then got a few injuries in a row, lost intensity in the gym and now have more fat than I want!

I'd say I average less than 1 drink a month.

Drink more. You'll gain weight.