Would it be usual to have the male quite a bit younger? I thought that was the problem with the lions?
Well if they'd chosen a mature male, then there's a good chance she'd have been killed by him... She's humanised to a point where a mature male might not tolerate some of her behaviours. But I think the theory with this male is that he's still young enough to be in the "cubby" phase of mind (in other words - just wants to play rather than do anything else) so there's a better chance of it being successful...
Obviously breeding is another matter (he won't be mature enough for that for at least another 18 months or so) and it's possible he'll still have to be exchanged in the future if a similar situation happens as it did with the lions. But hopefully by then she'll have picked up a few more tiger social skills from him by then... so time will very much tell