Comparative adjectives require a than before the thing that we are comparing with. The words younger and taller are both comparative adjectives, and we need to use than after them.
Senior can have a meaning similar to older. However, it's not a comparative adjective. The comparative construction for senior is more senior than. The normal adjective senior takes a preposition phrase headed by to:
- He is senior to me.
- He is more senior than me.
Different is also not a comparative adjective in the grammatical sense - although we do use it to compare things. When we use it on its own, it takes a preposition phrase headed by from, or occasionally to. Notice that different doesn't mean more different. If we use a comparative like this, then like with the other comparatives, we need the preposition than:
- She's very different to me.
- She's very different from me.
- Those twins are more different than these ones.
If we use different adjectives in one sentence then we need to use the correct preposition for each adjective. If the adjectives take the same preposition then we can sometimes omit the first preposition:
- Bertha is senior to and cleverer than Bob
- Bertha is older [than] and cleverer than Bob.