If anything, we would be out of pocket - an Over 75 would be going on an Adult ticket. It's this bit in United's latest communication that worries me:
"It is important from both a security perspective, and to mitigate against increased cases of ticket touting, that we are fully aware of each attendee in the stadium at every match. Please note that transferring a ticket in any other way (for example sending via WhatsApp) is not authorised, and will result in the attendee being refused entry to the stadium."
If for whatever reason a steward does decide to check, the old chap could be turned away trying to use his daughter's ticket. Seems mad, really, but I suppose it's a risk many will be taking as sharing tickets with close family is very common - and I doubt everyone is going to sign up for official membership.