When did Motley Crue become classic rock?

After 20 years anything can be considered vintage or classic by some.

Around the same time Nirvana and REM became Classic Rock. I'm sure many other bands are destined to become Classic Rock in the coming years. Some of those bands may included Radiohead, White Stripes, Porcupine Tree, The Strokes, Mastedon, etc.

For me, the definition of Classic Rock differs greatly from others; The Doors, Steppenwolf, Led Zeppelin, The Who, Cream, Mountain, Deep Purple, Jimi Hendrix, etc...now that's how I define it. I remember about 30 years ago hearing some DJ's saying things like "now here's a future classic rock song by Tom Petty". That song was "Free Fallin". I guess he was right, but at the time I thought his claim was ridiculous ;)

When their male fans start developing erectile dysfunction and their female fans become menopausal. I was never a fan of Motley Crue and I have no intention to waste time listening to their music, but there are others who think they are the best band since sliced bread. To each their own. Other people's classic rock may be my classic junk and vice versa.