"I was given my Lola back in October and I absolutely love her. I was told she is about 4 years old.
Can I bring in another baby/young guinea pig to keep her company?"
It's never too late to introduce a single pig to a new friend. In fact, many older pigs respond more positively to a younger companion - with their smaller size, an established pig is less likely to view the newcomer as competition or as a potential threat to their social standing. Of course, that's not to say that pigs of similar age or size won't get along. Like people, bonding depends more on the individual pigs and their personalities. You never know who may hit it off.
I've been getting similar questions from other cavy owners. The basic story: a piggy parent finds out that guinea pigs are highly social creatures who thrive in the company of their own kind. They want to find their pig a friend but they're not sure how their pig will react. Often they've been told by misinformed pet store employees that guinea pigs will fight. Or they've read a few anecdotes of pigs not getting along. There's even a myth that male guinea pigs can't live with each other. Not true! Just look at Orange County Cavy Haven's Boars Rule campaign.
To start you off, Jackie's Guinea Piggies has useful info and advice on guinea pig socialization. The guidelines listed under "Introductions" help to ensure your pigs can start off on the right foot (or paw). The "What to Expect and When to Intervene" section has tips, photos, and explanations to help illustrate cavy behavior.
If you're still apprehensive about the bonding process (totally understandable!), I'd highly recommend getting in touch with a guinea pig or small animal rescue. They generally have ample experience pairing up single pigs and can help make the process easier for you with personalized piggy "play dates".