Well,you'll first have to find out if he is a group centered individual or likes to go at it alone?Group-centered sports like baseball, rugby, soccer etc. will only get him bored if he unable to "shine" as an individual.
They may also fail to ignite his spark if he is more of a loner personality as they require a team oriented approach and a social nature.
He has Moon/Venus in Cap and Virgo respectively, so my guess is NO. He is not the "team spirit" kind of kid.
If he is more individualistic, then sports like cross country, tennis, swimming etc. are likely to interest him.
In these sports, the individual pushes themselves.
I liked these kinds of sports as a kid as I wasn't a socially inclined person.(I have Moon/Venus in Cancer/Scorpio respectively)
Also, his Venus/Moon in earth makes him more serious and likely to take activities of this nature(intended for fun and relaxation) a little more seriously.
Does his Mars in Gemini square his Venus? This could be indicative of a short attention span to Venus-related activities and an inability to focus.
Well, that is until he finds a balance between the need for constant change and stimulation(Gemini) and doing the activity to the best of his ability(Virgo).
Ask him about how he feels about those sports that I mentioned(the individualistic kind).But he is 7 years old and so, I would take my time.
The Mars in Gemini just needs to balance with Venus in Virgo. And with the Moon in Capricorn, he will attach himself quickly once that niche sport is found. Trust me on this.
And then, you'll have very little to motivate or push him on with as he'll be doing it all himself.