Hi and welcome, and sorry for the loss of your piggy.
Assuming you are adopting from a rescue, any good rescue will welcome the chance for you to bring Jellybean along to date with one of their pigs, and a good match will go on personality, not age. Whilst there's no right or wrong in age, babies are often (not always) easily accepted and will become the natural under-pig. However an under-pig may wish to become dominant when she hits the 'teenage' hormones and the once-happy pair can then fall out. Most matches done this way with sows stay happy, but there is a chance of the dominance struggle occurring so no-one can be sure of the outcome when bonding and adult and a baby.
However, when you get a successful bind between two adult pigs, their characters and preferences in hierarchy have already been formed, and are less likely to change. A successful match at this stage is likely to stay harmonious.
Illustrated Bonding / Dominance Behaviours And Dynamics
Introducing And Re-introducing Guinea Pigs
I have requested that this thread can be split in order for you to have your own thread. That way more people will see your post to welcome and advise you