With Electrum wallet, in its newest versions, the wallet software by default settings will give users Segwit addresses.
If you have a legacy seed phrase and you import it, electrum will give you legacy addresses.
You can't generate segwit addresses from a legacy seed phrase at all.
If you want to have Legacy addresses, you can import your wallet seed, and choose BIP39. You can type the mnemonic seed, choose BIP39 to try. If it accepts, you will have three options to import, as written in this guide,
Restoring your standard wallet from seed.You can't specify the addresses type, if the seed phrase has been generated by electrum. As already said by Charles-Tim, electrum seeds contain a version number which determines the seed type.
If OP has a electrum seed phrase and import it as a BIP39 seed phrase, he can specify the addresses type, but it won't give him the correct wallet.
You should be careful, it only works like that for Electrum version 2.0 and above. Electrum 2.0 has been released in 2015 AFAIK so OP's wallet could be, and it is very likely in my opinion, an older version using older seed format.
Starting with version 2.0, Electrum seed phrases include a version number, whose purpose is to indicate which derivation should be followed in order to derive private keys and addresses.
https://electrum.readthedocs.io/en/latest/seedphrase.html@Zargion if you are able to access your old wallet, try export your xpriv key (master private key) or the private keys of your addresses instead of your seed, with the GUI features or commands in the console. Or if you can't, try to just send your funds to a fresh wallet.