What was your first Sci-Fi game? How old were you when you play this game?

Probably X Com. But Rayman Raving Rabbids might be a Sci-Fi.

An Atari game I bought with the computer... Star Raders.
1981 or 82... Should make me about 20.

Probably Xargon's Revenge. Or if you're limiting it to adventure games, The Time Machine by Brian Howarth. In both cases when I was around 6 or 7.

The first I remember...

Rendezvous with Rama. Based on an Arthur C Clarke novel. Mid-80s. I would have been 9 or 10.

Since this is an IF forum, i recall reading a CYAO sci-fi book aimed at teens when i was a very young. Prolly early 2000s. I still remember the overly polite robot buddy though.

When it comes to actualy videogames, the earliest thing i recall is LEGO Star Wars. Which is really recent compared to the rest of you, which puts either me or my leaking memory to shame.

Well, my first sci-fi game was probably ratchet and clank, which not many people have heard of. It was really hard because I played it when I was about 7 or 8. It's kind of violent for a kid to be playing, but it's perfectly fine.

*Malevolent laugh

The earliest Sci-Fi game I can recall is Star Trek. (The text version) This was somewhere around 1979 or 1980 after I bought my first computer - an Exidy Sorcerer. Originally I had to type it in from a listing in a magazine but later I found it as a cassette tape that could be loaded up. Prior to this I think I had a simpler version that I could play on my TI 58 calculator, but I can't find it nor remember much about it. I vaguely think it was some sort of Moon or Mars lander. Nort sure if this qualifies for Sci-Fi though.
I would have been around 25 at the time for Star Trek but probably about 19 for the TI 58/59.