Are they boars or sows? I will link a guide in below that talks about the levels of dominance. There will be some rumble strutting, chasing and squealing in submission (from the younger one) which is all normal. You have to be careful not to break it up too quickly.
What you have to do is make sure the introduction is done in a neutral place - neither of them should have spent any time in it. Once they’re bonded you have to thoroughly clean the cage and rearrange it before you move them back in. Setting of the hierarchy will continue for a further two weeks. You have to be sure to see to the dominant pig first - it’s essential you respect their hierarchy.
Have you had the young piggy a while or just getting him? Piggies younger than 4 months need that social interaction more than ever, so quarantine can be skipped for them. Have a read of the guides below so you know what you may see.
One last thing - if your piggies are boars then be aware that bonding can be a little more difficult when in their teenage months (4-14 months).
Dominance Behaviours In Guinea Pigs
Bonding and Interaction: Illustrated social behaviours and bonding dynamics
A Comprehensive Guide to Guinea Pig Boars
Sows: Behaviour and female health problems (including ovarian cysts)