I'm playing Baldur's Gate on TuTu for the first time and I'm looking to dual class Imoen into a mage. She is my only thief. I'm curious if her 80 lock pick and 75 detect trap at level 5 will be sufficient later on?

You'll probably need to use potions or knock spells in a few areas yet.

Thieves level fast, you could wait until level 8-10 before dualling her.

i always dual Imoen when she reaches level 7 so i can get 100% on both Find Traps and Open Locks

If you don't have another thief in the party you'll be in a lot of pain without someone to handle the traps during the dualing period, afterwards you should be fine.
Detect traps is more important than open locks, locks can be retried, bashed or opened with knock spells.

Thanks for the replies guys! I am now wondering if it is reliable for my party's cleric to use detect traps, instead of having a 100% traps skill?

For Baldur's Gate you don't need 100 traps or locks skills, the locks and traps aren't that difficult. 75 skill should be enough to handle everything in the original campaign and most if not all the disarmable traps in the expansion.
The cleric spell is more comfortable because you get a message when exactly the trap search happens but be aware that you still have to disarm them which usually requires requires a little more skill than finding them.

All in all I'd rather use a thief, Find Traps doesn't last long and I prefer using the 2nd level spell slots with that more Hold Persons ... ;)