Unfortunately, for my bun, I had no idea what her age was, I just knew she was under a year, thats all they told me, so I fed her straight timothy pellets. Turns out, she was 4-5 months when I got her! So preferably I think alfalfa based is better for the young ones but it wont hurt them if you feed timothy pellets. She turned out just fine! And frankly, she enjoys her timothy pellets rather than the ones that have alfalfa mixed in them.
Let him eat as soon as he gets home, he needs food in his system from not eating during a days worth of surgery.  
It is possible he could be a mix.

Mine has always eaten timothy based pellets, since I got him anyways, and he is fine… I also only ever gave him alfalfa hay once. I think he was possibly 3-5 months when I got him. I use to give him 1/3 cup of pellets, now he gets 1/5.

I would have the pellets out for him when he gets home, maybe some vegetables if he has been introduced to any yet.

Mine eats his pellets in the morning, then around 5-7pm I give him 2 cups of vegetables. But you can wait till he feels better to get him on a feeding schedule.

He looks like a lop in the picture.

Yes, that is fine.

I changed mine over around that age. Oh and congratulations on finding a bunny! Of course this means you must tell us what he’s like and post pictures  

You’re going to want to find out what he’s currently eating and transition over a month, so by then he’d be ready for timothy pellets.

Looks like a broken lop.

Well either way, you might want to ask if you can buy a months worth(half a month, really) or buy enough to last yourself

Monkey had timothy pellets from day 1. She HATED alfalfa. So should be fine

MB, Sammy was the same way. Started Adult Bunny Basics T by Oxbow from the get go. Herself is healthy with an attractive girlish figure.