People argue about that all the time. Some say yes, others say no. When it comes age, I would say 20+ (twenty plus). Some people go even further and would say, "I am 20 and 1/2." And there are people who simply say, "I am twenty," until they actually turn 21 on their birthday(s).

Yes, unless you are doing math then you use above 20 for >20 and equal to or above twenty for ≥20

Hello. Yes it includes 20. Usually to specify you say 20 and above.