I was watching a 1971 episode of the detective series Public Eye today and I was surprised to see Colin Baker in a small role as a Town Hall clerk.
Looking up Colin's filmography on imdb shows this was only his fourth ever role on television, coming even before his first taste of fame as Paul Merroney in The Brothers
His scene is less than two minutes long so you're not missing much, but here's a look at the 28 year old Sixth Doctor.
So he's roughly the age of Matt Smith here. Gotta say on looks alone, I'd have preferred this version of Baker to have been the Doctor. Hmmm, suddenly I'm liking the Matt Smith choice even more.
The Gallifreyan Embassy - Forum