Hi!
Age is not as relevant as mutual liking and character compatibility. If you can, please consider rescue dating so you come home only with a new lady if acceptance has happened so the biggest hurdle is out of the way and you have the rescue to fall back on if things go haywire at any stage. It may be more effort but on the other hand, you can neatly avoid all the usual pitfalls that await the unwary and have the nerve-wracking bit of the bonding happening under expert supervision.
Your closest good welfare standard rescue that offers dating is Ayr Guinea Pig Rescue. It may be worth contacting them via Faceook now.
Rescues, Shops, Breeders or Online? - What to consider when getting guinea pigs (also contains a chapter on rescue dating)
Rescue Locator
@Julie M (who is connected with the rescue)
As to intros:
Piggies under 4 months (sub-teenagers) are desperate for company and should be introduced very quickly. You can give them a few hours in a divided run, if necessary. Over 4 months (teenagers or adults), it is better to give them time to settle next to each other.
Please follow our our comprehensive step-by-step bonding guide, which takes you through all stages of the complex bonding process (including the run-up) and also has got chapters with videos on mixed pairs and baby bonding. You will find it very helpful:
Bonding and Interaction: Illustrated social behaviours and bonding dynamics
Further information in mixed gender pairings and sow behaviour:
A Closer Look At Pairs (Boars - Sows - Mixed)
Sows: Behaviour and female health problems (including ovarian cysts)
When Sows Experience A Strong Season (videos)
I hope that this helps you?