Age: I think canonwise he's about 250-300? It is really difficult to pinpoint his age haha, let's say 275.
Personality:
He doesn't tend to get involved because he believes that, no matter what he does, he won't be able to change history, and that trying would be a lesson in futility, as he explained to Barbara when she tried to change the Aztecs. Whether or not he can alter the timeline, he believes he is dutybound not to. There are occasions where he will, but this usually happens because he finds himself stuck in a situation where the only way out is to fight, for one side or the other. Self-preservation seems to overrule his sense of duty.
He is far from modest. Often he can be heard tooting his own horn about his intelligence and his superiority. However, he tends to prefer helping others learn for themselves, testing their own minds and ways of thinking. He seems to think others races need to be taught, and takes it upon himself to do the teaching, trying to guide them towards the right path rather than leading them there by the hand.
Having never really been alone in his life up to this point, it's difficult for him to be content as a solitary person over long periods of time. He'll seek out companionship, winding up with someone to travel with - first his granddaughter, then Ian and Barbara. It can take time for him to warm up to someone, seeming distrustful or callous at first, but in time they'll grow on him and he'll be more forthcoming, more willing to help them understand things, so long as they don't ask too many foolish questions.
He has a problem with common ground - since he grew up on Gallifrey, has many years of experience in the galaxy, and is well older than any human, or some other species for that matter, it can be difficult for them to see things the same way as him, to understand how things work. Many don't share the same interests, and it can be difficult to make friends with someone who seems to have nothing in common with you - if it weren't for his adventures, and those he winds up with enjoying the thrill of travel and the unknown, he'd likely travel alone. And he knows that he'll far outlive those around him, so can be reluctant to become to close to others. He feels out of place in much of human society, and this puts a damper on his willingness to connect.
The human population has promise. There's nothing inherently wrong with them. They're young, and this comes with all the problems of youth - they're judgemental, impresionable, rash, impulsive, and have difficulty seeing beyond their own scope of vision. Much of humanity would sooner see an alien tested on in a lab than make friends with them.
As to being human himself... He likely won't believe it ever. He'll laugh it off. If proof is ever shown, however, he won't take it well - how does one handle being proven that their entire life was a lie? With difficulty. Especially for someone who always thought he was superior to humanity - to find out he's one of them, he's one of the young race of rash and judgemental people he's always held to be beneath him - it will be quite the discovery, and will be very difficult for him to overcome. He will likely try to excuse it - the tests were faked, something was done to him to make him human, perhaps the body he's in was a clone made to look like him - whatever he can until there really is no way to continue claiming it as a falsehood.
City Proof:
I was going to include a photo and forgot to add it in :( So yeah, let's go with that. Maybe a family photo of him and his children/grandchildren?
Re: Revisions (SORRY had to repost due to italics fail)
Age:
I think canonwise he's about 250-300? It is really difficult to pinpoint his age haha, let's say 275.
Personality:
He doesn't tend to get involved because he believes that, no matter what he does, he won't be able to change history, and that trying would be a lesson in futility, as he explained to Barbara when she tried to change the Aztecs. Whether or not he can alter the timeline, he believes he is dutybound not to. There are occasions where he will, but this usually happens because he finds himself stuck in a situation where the only way out is to fight, for one side or the other. Self-preservation seems to overrule his sense of duty.
He is far from modest. Often he can be heard tooting his own horn about his intelligence and his superiority. However, he tends to prefer helping others learn for themselves, testing their own minds and ways of thinking. He seems to think others races need to be taught, and takes it upon himself to do the teaching, trying to guide them towards the right path rather than leading them there by the hand.
Having never really been alone in his life up to this point, it's difficult for him to be content as a solitary person over long periods of time. He'll seek out companionship, winding up with someone to travel with - first his granddaughter, then Ian and Barbara. It can take time for him to warm up to someone, seeming distrustful or callous at first, but in time they'll grow on him and he'll be more forthcoming, more willing to help them understand things, so long as they don't ask too many foolish questions.
He has a problem with common ground - since he grew up on Gallifrey, has many years of experience in the galaxy, and is well older than any human, or some other species for that matter, it can be difficult for them to see things the same way as him, to understand how things work. Many don't share the same interests, and it can be difficult to make friends with someone who seems to have nothing in common with you - if it weren't for his adventures, and those he winds up with enjoying the thrill of travel and the unknown, he'd likely travel alone. And he knows that he'll far outlive those around him, so can be reluctant to become to close to others. He feels out of place in much of human society, and this puts a damper on his willingness to connect.
The human population has promise. There's nothing inherently wrong with them. They're young, and this comes with all the problems of youth - they're judgemental, impresionable, rash, impulsive, and have difficulty seeing beyond their own scope of vision. Much of humanity would sooner see an alien tested on in a lab than make friends with them.
As to being human himself... He likely won't believe it ever. He'll laugh it off. If proof is ever shown, however, he won't take it well - how does one handle being proven that their entire life was a lie? With difficulty. Especially for someone who always thought he was superior to humanity - to find out he's one of them, he's one of the young race of rash and judgemental people he's always held to be beneath him - it will be quite the discovery, and will be very difficult for him to overcome. He will likely try to excuse it - the tests were faked, something was done to him to make him human, perhaps the body he's in was a clone made to look like him - whatever he can until there really is no way to continue claiming it as a falsehood.
City Proof:
I was going to include a photo and forgot to add it in :( So yeah, let's go with that. Maybe a family photo of him and his children/grandchildren?