I'd ask if they knew what they were getting. If you pair a younger and an older person, there is going to be friction. That can be good or bad.
If you want to stabilize a young genius (you know the type: Reckless, fearless, prone to making "small" last minute changes to code that is about to be installed in production), then pairing him with an experienced buff can make things easier for everyone. But both people must understand what the goal of this setup is. Otherwise, they'll just freak each other out.
If they know the shop knows they lack experience and want to learn from you, good. If they have no time, just need another pair of hands and there is just 0.2% blood left in the adrenaline system, things will become unpleasant eventually (you will seem to be "slow" while they will look "stupid" to you).
From my personal experience: I once worked with a guy who was 30 years my senior (not retiring next year but not too far off, either). He knew the system while I was pretty green. OTOH, when I found something that was important, I would bug him to fix it until we could do it. That meant we never broke the critical things during production hours but we also started to change things; older people lean towards "if it works, don't touch it" which causes the whole system to rot. So it was win-win but mostly because our manager clearly stated "I want you two to work together so we make progress but not the wrong kind."