General

Is 20 years old too early to start gaining?

Not really. I have at work two guys who I guessed they are your age and your size. And I went to school with a guy of similar size to you.

Plus on the female size a former gf who was never below 100 Kg as an adult weight and at a previous job a female colleague at 23 well above your size.

Probably a good thing since you can build strength while you gain.

Is your gf following your gain?
7 months