I've no idea how long it would take me to grow a moustache. I've had mine for about 30 years and it's only even been shaved off twice in that time (once when a trimming got out of hand and I ended up looking like Adolf Hitler and once because my wife wanted to see what I'd look like).
I've always wanted to grow a beard but as I've been in the military for over 25 years that's not been an option. Once, after 3 back-to-back tours in Iraq I found myself with an obscene amount of leave that I had to take all at once (about 4 weeks) so decided to give it a go. It was at this point that I realised I'd left it too late, the beard grew very rapidly and with even coverage

the problem was it was a sort of stripy Badger style mix of black, brown, ginger and grey
