He told The Sun newspaper: ''I feel a bit for Harry. At his age I was in this lilywhite boyband, Take That.
''But I was meeting up with mates, jumping out of the tour bus and into a Transit van at motorway service stations all around the country. No one had a camera phone.''
Harry, 18, is extremely popular with the ladies, something Robbie can identify with.
He continued: ''It's only natural a lad in a boyband will be compared to me at some point.
''Everybody is a ladies' man or a man's man, whatever your persuasion might be. He's just having a nice time.''
But the star admitted he is slightly envious of Harry's youth and what he has to look forward to.
Robbie added: ''I see Harry through bitter-getting-old-and-married-and-can't-do-all-of-that-any-more eyes.
''Also, I've got a lot of love for him and One Direction. On the pie chart, the love outweighs the bitterness -- but the bitterness is in there too.''