While not as young as Peter Davision when he took on the role of the Doctor, David Tennant is a young 34. He will probably need a 50+ year old companion after Billie leaves the show in order for WHO to be in compliance with this new legislation.
John Barrowman is only 38 which means that the mysterious "Gwen" of Torchwood will have to be recruited from the geriatric set as well. So we obviously can't trust all these rumours about RTD trying out teen pop singers for the part. Nope it looks like the writing is on the wall, Gwen will be played by Angela Lansbury.
PS - Torchwood was unveiled as a sexier version of Doctor Who, but I wonder if it will ever get as kinky as this film.