'If men can date younger women, why can't an older woman date a younger man? It's sexist,' Sean, 32, told TMZ when asked about the age gap.
'It's about the person she is inside,' he added. 'Age is just a number. If there's a connection and someone cares about a person, that's what matters really.
'I'm very happy. She's a very very very good lady.'
Sean, son of rocker Rod Stewart and his ex-wife Alana Hamilton also dismissed rumours he had moved in with the mother of three.
'I actually have my own place,' he said.
Earlier this week, Adrienne discussed her blossoming relationship with Sean, revealing the romance is in its early stages.
She told People.com: 'This started as a business relationship and now we're casually dating. It's casual, real casual.'
Adrienne, who split from husband of 10 years Paul Nassiff last summer, also defended Sean's party boy reputation, describing him as 'a lot more mature than a lot of 60-year-olds at this time in his life'.
She said the former Celebrity Rehab star has turned his back on his partying ways, explaining: 'That was when he was a young kid. He's been clean and sober for years.'
Adrienne described herself as a 'modern businesswoman' in the interview saying: 'I don't think of age.'
She also said she appreciates Sean coming from a famous family because 'he understands my world,' adding that Sean's rocker father Rod, 68, is 'lovely... a very nice person'.
Loved up: Adrienne said that the pair are taking their romance 'very casually'
They held hands and Sean planted a kiss on the reality star's cheek as they left the eatery.
The witness said: 'They looked really cute and comfortable together, definitely like they’ve known each other a long time.'
Family business: Adrienne with her children and then-husband Paul Nassif in October 2011