Maybe some good old testosterone only for 12 weeks?
Definitely do some bloods before as at 50 you might already be on the lower side and recover could be a bit tricky.
Also remember 4 months is nothing, I have been training for 25 years consistently, others guys on here far longer, when im wanting to be 'larger' it comes down to the amount of food i eat and I use heavier weights, or to be leaner, more cardio, clean food, more reps, less weight. The biggest thing is consistency, not throwing drugs around. A younger guy we would probably say train naturally for at least 2 years and progress takes time.
"Whether You Think You Can or Can't, You're Right"--Henry Ford