ddt
Mafia Penguin
Just to add to the confusion I think Abdul is nearly right, Giraffe is wrong, and conmmandlinegamer and DC are right so it should be:
Onkel Adolf ist heute hunderteinundzwanzig* Jahre alt
* He would have been 121 and numbers in German are written as one word, no matter how long
To throw in my two cents, what about:
Onkel Adolf wäre heute hunderteinundzwanzig Jahre alt
It's not a real event, the guy is dead, so the past subjunctive (Konjunktiv II) is the appropriate tense for the verb.
And you could also say "einhunderteinundzwanzig". That's very customary in Germany to say at least when counting money - for emphasis, you say "one hundred".