Its a wonderful hormone and should be called 'Repair Hormone' once you are over 18 years old or so.
To get real HGH you have to have a documented very low GH production .. this is all nonsense based around fears that people in our 50s 60s and above are going to suddenly start cheating and breaking Olympic records or challenging Barry Bonds Home run record .. :-)
It is a very safe hormone when used properly in small physiologic doses to restore true deficiency. It has profound effects on re-hydrating skin, organs, bones, muscle and has equally, if not greater, effects on emotional stability and sense of well being.
L -GLutamine can indeed help increase night time release of GH when taken- 2 to 4 grams just before bed.
Also a new effective sublingual Secretagogue called 'Secretropin' shows real promise, even in people over 50! Most people over 50 don't get much lasting benefit from most amino-acid based Secretagogues don't work very well.
Same with intense interval training. Yes, it will help boost short term excretion of GH some in older folks, but not nearly as much as in younger people doing the same excercise.
The very best Secretagogues are replacement doses of testosterone for both men and women, Melatonin for both sexes and estrogen for women. Also restoring adequate thyroid and DHEA can help as well.
The gold standard is recombinant DNA injectable Human GH but in the US it isn't so easy to qualify and it is very expensive.