In a word, no. Any claims from any source that this is possible are false advertising and should be ignored.
This is not to say it isn’t entirely possible without steroids in 9-10 years, though, which would require a dedicated bodybuilder putting in the hours in the gym every day, with a very clean diet and taking anabolic steroids at higher doses than most natural athletes do. At 62kg, this person would have less muscle mass than the average male (~73kg), so it would take longer for him to gain. This might not be “20kg” of lean muscle by some people’s standards, which accounts for the HST [Hypertrophy Specific Training] study by Schoenfeld et al. that found it took 20 weeks for the bodybuilders to gain 20kg of lean muscle.
However, I’m fairly sure any claim of naturals gaining up to 1lb per week is false – if true, other athletes could achieve similar results with much less time in the gym. Frankly, there are very few “naturals” who live up to these claims anyway, even under optimal conditions. Those who make such claims are likely on steroids or are incredibly gifted genetically (those two aren’t mutually exclusive).
If this person was taking anabolic steroids and eating enough food, they might be able to gain 5-10kg (~11-22lbs) of lean muscle in a year at 62kg and maintain most of it after they come off, but this is entirely theoretical and would depend on their genetics, age, body fat percentage when starting and many other factors.
It’s also worth noting that it doesn’t matter whether you gain 10kg of muscle or 20kg in a year – if you’re much smaller to start with, you will still look big when you’re done. Gaining 20kg in a year (~44lbs) is going to make most people look very impressive – especially considering the lack of drugs used in the HST study by Schoenfeld et al., which was conducted using naturals. This isn’t entirely true for experienced individuals who have been lifting weights for years, though, where 5-10kg (~11-22lbs) might make more of a difference.
It’s also worth mentioning that it takes much longer than 12 months to completely ‘transform’ your body – you won’t look like Schwarzenegger in the early stages (I wish I had his genetics), and looking more muscular usually just means you’re waiting for it to get even bigger. If your diet is sub-par, this could take up to 3 years. If your exercise routine isn’t very efficient for gaining muscle, it will take even longer than that too.
Long story short: if someone claims they gained 20kg (~44lbs) of muscle in 12 months without steroids, they are either on steroids or lying – at least, unless their starting weight was under 60/132lbs (that seems to be the magic number).
The only exception to this is if they gained 20kg in 11 months and two weeks; however, that would still require them to be on anabolic steroids. If someone was able to gain 20kg of muscle in a year without drugs but not in 11 months and two weeks, their starting weight must’ve been over ~75/165lbs (which seems to be the magical cutoff point for drug-free muscle gains). Anything lower than that, and it will take longer than one year unless you start taking steroids which speeds up everything by a magnitude of ten.
If your current body weight is below 60kg (~132lbs) and someone tells you they got as big as Schwarzenegger or any other famous bodybuilder without drugs, they’re most likely lying. If you want to lose weight and look like an ordinary person (no matter how skinny) with visible abs and some lean muscle mass, it’s possible; however, gaining 20kg of muscle in a year isn’t realistic for someone who has never lifted weights before.