I'm 62 and on 1.25 iu eod for last year.
My last blood testing showed IGF of 284.
The range is 71-290, so I would say this is very good.
I normally take the HGH together with testosterone and amiridex within my HRT program.
I really don't know what level a 20 year old would have except for the language on the blood test about "Tanner Stages". A fast look at Google says this refers to children entering in and in puberty. We sure wouldn't want that. These growing, maturing kids were expected to be as high as 839.
I'd think that being at the top of the range ... around 300 ... should be sufficient for our needs.