I've had 'em since I was 15
The current sideburns trend has been around since 1995. Before then, it was distinctly uncool to be seen with sideburns, and would elicit a lot of "That guy thinks he's Elvis" comments. I wouldn't say the 70's are back. 70's style sideburns were really thick, and were wide at the base. The kind that's popular with most guys under 30 these days is the thinner, more rectangular type. And most Hollywood celebrities have 'em too.
BTW, not having sideburns is lame, IMO. Makes you look like a kid :Q