Is it normal for my 40 y/o husband to text/hangout with teenage girl?

I feel silly asking this question as my husband says I'm "wacked", what ever that is supposed to mean. As far as I'm concerned feelings should be respected. My husband works at an ice facility (arena)where there are young teenage girls that work at the consession stand,some guys as well. It has never bothered me until the other day when we were to go out on a family visit with my parents, all day he kept trying to talk me out of it, lets go another day. I already promised to take our son to see my parents I told him..he said he was tired and just wanted to relax at home, so I decided to go by myself,no big deal. 1 hour later he texts me saying he's going out for a bit, I text back later asking where did you go? He says he's just checking a girls (co-worker) brakes, (she has a father, but says he's useless at mechanics)don't have a problem with that, just the fact that he said he wanted to stay home so he could "relax" which usually means watching tv all day. He even took the time to got to the library and get a manual on her make of car. I never said anything, although it did bother me a bit. Next evening was woken up by my husbands text alert going off at 11:30,after I went to bed at 11:00 he sent her a text asking if she had her brakes checked by her high-school auto shop, what was she doing, telling her he's watching a movie etc. later that night I told him I thought it was odd that he waited til I went to bed to text her..he said she's a friend/co-worker, she comes to work even when she's not scheduled to work to "hang out" with him, he told me this himself. I found that even more strange, he then said she's like a sister, I said more like a daughter with 23 years age difference. C'mon I'm not that stupid. He says she's over weight and is strong like a guy, she helps me at work sometimes lifting stuff. He's not attracted to her. He said I could have a teenage male friend as long as he was fat and unattractive. WTF..I'm 42 years old. In the end I basically told him I thought that it was inappropriate to have a teenage girl as a friend, what could you possibly have in common, other than that you work at the same place? and to be texting her almost every day. He replied "wait til I tell her how you feel"..and then laughed. Okay now I'm furious. Now he's not talking to me, very childish. He thinks I'm saying that he wants to sleep with her. (not true)It's the age difference principle... What do I do now? Sorry for the very long story!