The father of my child owe's me over $60,000 in child support. He is working under the table in construction and lives in another state, so it is near impossible to collect on child support. He did serve in the Navy for 7 years. Can his Navy retirement be garnished for back child support owed?

Yes it is but it's not an easy thing to accomplish by yourself. You need the court order first and then know where he lives now and hope that he IS collecting he pension, If you know he's collecting the pension that's half the battle.

? Is there a navy retirement with only 7 years of service ?

I have an assumption that you have to have a min of 20 years in the US military to collect any retirement what so ever ?

That is correct.