Highest rank was Supreme quickly fell down back to DMG though, the people there are either way cheating or way to good for me who knows xD.
Took about 5 years? Spend my first two years on silver cause my pc was trash and I played with 30 fps max on dust2 (the old one) in 2015 to 2016. After I actually got my new pc I started getting fast into gold nova niveau which was a golden moment for me (finally getting out of silver and seing that gold nova 1 rank up was so special to me and non the less I screamed like crazy back then when I ranked up, today it is more the opposite xD)
After that I managed to get a hold in MG1 - MG2 and then climbed the ranks fast until like I said reached Supreme and lost the fun cause I got kicked in the ass every Match.
RE: What rank are you, and how long did it take to get there?
Highest rank is Gold 1 (now). I've been playing CS for many years but I didn't play competitive. It took me like 2-3 weeks cause I had to balance it with studying