By age 55, your body's own growth hormone output is likely on the low side. After 21 it begins to fall, dropping roughly 14% with each decade that passes. One route is to spray and pray — begin at 2iu and gradually increase — or, if you lean toward harm reduction, get labs done. IGF-1 blood tests are fairly inexpensive and can be ordered online. Testosterone, as another person pointed out, is also on the table. For me, stacking HGH with Testosterone left me looking and feeling better at 47 than I can ever recall. I will never stop taking either.
Based on what I've personally seen, the GH secretagogues produce nothing you'd notice. Even if they raise your levels by 30% (which isn't typical), 30% of nothing is still nothing.
Nothing will work if your sleep is garbage, you don't lift and your diet isn't dialed in.